ARM: pm: omap34xx: no need to save all registers in sleep34xx.S

The ABI allows called functions to corrupt r0-r3 and ip (r12).  So
its pointless saving these registers in the suspend code - the
calling function will expect them to be corrupted and so won't rely
on their contents after resume.

Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>