Improve __copy_to_user and __copy_from_user performance

Provide a __copy_from_user that uses memcpy. On BCM2708, use
optimised memcpy/memmove/memcmp/memset implementations.

arch/arm: Add mmiocpy/set aliases for memcpy/set

See: https://github.com/raspberrypi/linux/issues/1082

copy_from_user: CPU_SW_DOMAIN_PAN compatibility

The downstream copy_from_user acceleration must also play nice with
CONFIG_CPU_SW_DOMAIN_PAN.

See: https://github.com/raspberrypi/linux/issues/1381



Signed-off-by: Phil Elwell <phil@raspberrypi.org>