ARM: pxa: Add CLKSRC_OF dependency

Select CLKSRC_OF for PXA architectures.

Signed-off-by: Robert Jarzmik <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>

arch/arm/Kconfig

···
 	select AUTO_ZRELADDR
 	select CLKDEV_LOOKUP
 	select CLKSRC_MMIO
+	select CLKSRC_OF
 	select GENERIC_CLOCKEVENTS
 	select GPIO_PXA
 	select HAVE_IDE