Apply the same fix for 83xx as was done for 85xx in commit
96196a1f

.

Without this, NAND SPLs are built with the text base intended for the main
image, resulting in a broken, very large u-boot-nand.bin.

The block of defines for NAND boot is moved closer to where
CONFIG_SYS_TEXT_BASE is defined.  We can't directly use
CONFIG_SYS_NAND_U_BOOT_DST in the definition of CONFIG_SYS_TEXT_BASE because
autoconf.mk will include the literal text "CONFIG_SYS_NAND_U_BOOT_DST",
but at least keep them close and point out that they're supposed to be
the same.

Signed-off-by: Scott Wood <scottwood@freescale.com>