[ARM] 3113/1: PXA: Allow machines to override (and also reuse) pxa pm functions

Patch from Richard Purdie

Update the PXA pm.c file to allow machines (such as the Sharp
Zaurus) to override the standard pm functions but reuse/wrap them
where needed.

The init call is made slightly earlier to give machine code an init
level to override them in removing any race.

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