rtc: make rtc-omap driver ioremap its register space

The rtc-omap driver currently assumes that the rtc's registers are at a
fixed address and already mapped into virtual memory space.  Remove those
assumptions so the same driver can be used for similar devices that reside
at different physical addresses (e.g., TI's DA8xx/OMAP-L13x SoC's).

Also allow the possibility for the timer and alarm interrupts to use the
same IRQ.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>