[PATCH] ppc64: genrtc build fix

genrtc.c won't compile on ppc64.  Seems that ppc32 does support it though?

We do this wrong btw - we should be selecting GEN_RTC in each
arch/xxx/Kconfig.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>