ARM: pxa: add dummy clock for pxa25x and pxa27x

ARM: pxa: add dummy clock for pxa25x and pxa27x

gpio-pxa driver is shared among arch-pxa and arch-mmp. Clock is the
essential component on pxa3xx/pxa95x and arch-mmp. So we need to
define dummy clock in pxa25x/pxa27x instead.

This regression was introduced by the commit "ARM: pxa: add dummy
clock for sa1100-rtc", id a55b5adaf403c4d032e0871ad4ee3367782f4db6.

Reported-by: Jonathan Cameron <[email protected]>
Signed-off-by: Paul Parsons <[email protected]>
Tested-by: Robert Jarzmik <[email protected]>
Signed-off-by: Haojian Zhuang <[email protected]>