rtc: omap: let device wakeup capability be configured from chip init logic

The rtc-omap driver currently hardcodes the RTC wakeup capability
to be "not capable". While this seems to be true for existing OMAP1
boards which are not wired for this, the DA850/OMAP-L138 SoC, the
RTC can always be wake up source from its "deep sleep" mode.

This patch lets the wakeup capability to be set from platform data and
does not override the setting from the driver. For DA850/OMAP-L138, this
is done from arch/arm/mach-davinci/devices-da8xx.c:da8xx_register_rtc()

Note that this patch does not change the behavior on any existing OMAP1
board since the platform device registration sets the wakeup capability
to 0 by default.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>