ARM: pm: CPU specific code should not overwrite r1 (v:p offset)

r1 stores the v:p offset from the CPU invariant resume code, and is
expected to be preserved by the CPU specific code.  Overwriting it is
not a good idea.

We've managed to get away with it on sa1100 platforms because most
happen to have PHYS_OFFSET == PAGE_OFFSET, but that may not be the
case depending on kernel configuration.  So fix this latent bug.

This fixes xsc3 as well which was saving and restoring this register
independently.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>