arm: enable unaligned access on ARMv7

Recent toolchains default to using the hardware feature for unaligned access on
ARM v7, rather than doing the software fallback. According to ARM this is safe
as all v7 implementations have to support this feature.

To avoid CPU hangs when doing unaligned memory access, we have to turn off
alignment checking in our CPU initialisation code

Signed-off-by: Lucas Stach <dev@lynxeye.de>
CC: Albert ARIBAUD <albert.u.boot@aribaud.net>