Add get_boot_device and get_board_serial in soc.c.
Add is_recovery_key_pressing function definition
Use CONFIG_USB_GADGET and CONFIG_FSL_FASTBOOT to separate the usb related code
in the f_fastboot.c.The CONFIG_USB_FUNCTION_FASTBOOT should be defined So the
boota can work normally.

Change-Id: I6c0d3851ba28b147d0da310485a06f102de5a813
Signed-off-by: Zhang Bo <bo.zhang@nxp.com>