powerpc/ps3: Add rtc-ps3

Create a real RTC driver for PS3, and unhook the deprecated
ppc_md.[gs]et_rtc_time.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>