[ARM] 3011/1: pxafb: Add ability to set device parent + fix spitz compile error

Patch from Richard Purdie

Add a function to allow machines to set the parent of the pxa
framebuffer device. This means the power up/down sequence can be
controlled where required by the machine.

Update spitz to use the new function, fixing a compile error.

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