arm/arm64: KVM: MMIO support for BE guest

arm/arm64: KVM: MMIO support for BE guest

Do the necessary byteswap when host and guest have different
views of the universe. Actually, the only case we need to take
care of is when the guest is BE. All the other cases are naturally
handled.

Also be careful about endianness when the data is being memcopy-ed
from/to the run buffer.

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
(cherry picked from commit 6d89d2d9b5bac9dbe40ee106ceda9307b6265234)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>