arm: clear UNALIGN_TRP bit in CCR register

Clear the UNALIGN_TRP bit in the CCR register, if the config
CONFIG_TRAP_UNALIGNED_ACCESS is not set.

Despite the fact that the reset value of UNALIGN_TRP is 0, always clear
the bit. It is useful in double image systems. The new image can't rely
on settings left by the previous image.

Signed-off-by: Dawid Niedzwiecki <dawidn@google.com>