power: pm8921-charger: enable DCIN_VALID_IRQ as wake irq

When the device is in suspend the DCIN_VALID_IRQ is not
used as a wake up interrupt.

Fix this by configuring the DCIN_VALID_IRQ as a wake up
interrupt.

CRs-Fixed: 389524
Change-Id: If3c5f00f4b75d03838ee556235697369fd2e47dd
Signed-off-by: David Keitel <dkeitel@codeaurora.org>