rtc: rtc-omap footprint shrinkage

Shrink the runtime footprint of the OMAP1 RTC driver a bunch by removing
some old hacks and switching to platform_driver_probe().

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>