Add mx7 secure boot support, add helper macro IS_HAB_ENABLED_BIT
to get the corresponding bit mask per SoC (mx7 or mx6) to identify
if securue boot feature is enabled/disabled.

On authenticate_image only check for mmu enabled on mx6 SoC to
force pu_irom_mmu_enabled so ROM code can perform mmu cache flush
mx7 SoC ROM code does not have this issue as ROM enables cache support
based on fuse settings.

Signed-off-by: Adrian Alonso <aalonso@freescale.com>