davinci: cp_intc: provide set_wake function

There is nothing special to be done for interrupts
which can wakeup the device from sleep on CP-INTC,
but not having a set_wake implemented prevents use
of common drivers which expect this function to be
implemented for all wakeup interrupt sources.

This patch fixes the issue encountered when using the
omap-rtc driver on DA850. On DA850 the RTC alarm
interrupt is used to wake up the SoC from deep sleep
mode. Without this patch, the disable_irq_wake throws
an unbalanced wake disable warning while resuming
because the previous enable call fails for lack of
set_wake implementation.

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