rtc: stmp3xxx: Remove UIE handlers

The RTC core handles UIE since 6610e089

 (RTC: Rework RTC code to use
timerqueue for events), so remove the specific interrupt in this driver.
To make it work at all, enable interrupts in set_alarm() if needed. Drop
IRQF_DISABLED which is deprecated, while we are here.  Finally, add my
copyright after all these changes.

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>