ARM: mvebu: fix suspend to RAM on big-endian configurations

The current Armada XP suspend to RAM implementation, as added in
commit 27432825 ("ARM: mvebu: Armada XP GP specific
suspend/resume code") does not handle big-endian configurations
properly: the small bit of assembly code putting the DRAM in
self-refresh and toggling the GPIOs to turn off power forgets to
convert the values to little-endian.

This commit fixes that by making sure the two values we will write to
the DRAM controller register and GPIO register are already in
little-endian before entering the critical assembly code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: <stable@vger.kernel.org> # v3.19+
Fixes: 27432825 ("ARM: mvebu: Armada XP GP specific suspend/resume code")