define Z_NULL to (void *)0 include/u-boot/zlib.h to get rid of most of
the NULL pointer warnings.

inflate.c:942:1: warning: non-ANSI definition of function 'inflateEnd'
inflate.c:9:1: warning: non-ANSI definition of function 'inflateReset'
inflate.c:12:17: warning: Using plain integer as NULL pointer
inflate.c:12:42: warning: Using plain integer as NULL pointer
inflate.c:15:17: warning: Using plain integer as NULL pointer
inflate.c:21:19: warning: Using plain integer as NULL pointer
inflate.c:35:1: warning: non-ANSI definition of function 'inflateInit2_'
inflate.c:38:20: warning: Using plain integer as NULL pointer
inflate.c:41:17: warning: Using plain integer as NULL pointer
inflate.c:42:17: warning: Using plain integer as NULL pointer
inflate.c:50:18: warning: Using plain integer as NULL pointer
inflate.c:65:23: warning: Using plain integer as NULL pointer
inflate.c:69:21: warning: Using plain integer as NULL pointer
inflate.c:78:1: warning: non-ANSI definition of function 'inflateInit_'
inflate.c:86:1: warning: non-ANSI definition of function 'fixedtables'
inflate.c:108:26: warning: Using plain integer as NULL pointer
inflate.c:109:1: warning: non-ANSI definition of function 'updatewindow'
inflate.c:112:30: warning: Using plain integer as NULL pointer
inflate.c:339:1: warning: non-ANSI definition of function 'inflate'
inflate.c:349:17: warning: Using plain integer as NULL pointer
inflate.c:349:42: warning: Using plain integer as NULL pointer
inflate.c:350:27: warning: Using plain integer as NULL pointer
inflate.c:369:42: warning: Using plain integer as NULL pointer
inflate.c:376:32: warning: Using plain integer as NULL pointer
inflate.c:401:54: warning: Using plain integer as NULL pointer
inflate.c:419:32: warning: Using plain integer as NULL pointer
inflate.c:426:32: warning: Using plain integer as NULL pointer
inflate.c:433:32: warning: Using plain integer as NULL pointer
inflate.c:444:36: warning: Using plain integer as NULL pointer
inflate.c:449:37: warning: Using plain integer as NULL pointer
inflate.c:450:38: warning: Using plain integer as NULL pointer
inflate.c:457:40: warning: Using plain integer as NULL pointer
inflate.c:458:47: warning: Using plain integer as NULL pointer
inflate.c:480:40: warning: Using plain integer as NULL pointer
inflate.c:481:50: warning: Using plain integer as NULL pointer
inflate.c:491:37: warning: Using plain integer as NULL pointer
inflate.c:492:37: warning: Using plain integer as NULL pointer
inflate.c:501:40: warning: Using plain integer as NULL pointer
inflate.c:502:53: warning: Using plain integer as NULL pointer
inflate.c:512:37: warning: Using plain integer as NULL pointer
inflate.c:513:40: warning: Using plain integer as NULL pointer
inflate.c:525:32: warning: Using plain integer as NULL pointer
inflate.c:529:52: warning: Using plain integer as NULL pointer
inflate.c:543:54: warning: Using plain integer as NULL pointer
inflate.c:932:17: warning: Using plain integer as NULL pointer
inflate.c:932:42: warning: Using plain integer as NULL pointer
inflate.c:935:26: warning: Using plain integer as NULL pointer
inflate.c:940:19: warning: Using plain integer as NULL pointer
adler32.c:58:5: warning: non-ANSI definition of function 'adler32'
adler32.c:81:16: warning: Using plain integer as NULL pointer
zutil.c:53:9: warning: non-ANSI definition of function 'zcalloc'
zutil.c:64:9: warning: non-ANSI definition of function 'zcfree'
inffast.c:70:1: warning: non-ANSI definition of function 'inflate_fast'
inftrees.c:33:1: warning: non-ANSI definition of function 'inflate_table'

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>