rtc: stmp3xxx: Restore register definitions

The stmp3xxx driver used to include register names from a stmp-specific
include. Because of consolidation, plat-stmp has now been removed and
merged with the compatible mach-mxs. Restore the register names directly
in the driver and rename them to be specific to this driver.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Tested-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>