The powerpc arch uses CONFIG_PPC instead of CONFIG_POWERPC.  This fixes
drivers/rtc/Kconfig to use the correct config option.
Signed-off-by: NWade Farnsworth <wfarnsworth@mvista.com>
Acked-by: NJon Loeliger <jdl@freescale.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>