ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP

Newer versions of gcc generate unaligned accesses by default, causing
kernel panics when CONFIG_ALIGNMENT_TRAP is enabled. This patch adds the
-mno-unaligned-access option to gcc.

Reported-by: Ali Saidi <ali.saidi <at> arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas <at> arm.com>