leds: leds-qpnp: add blink functionality support for GPLEDs

Existing implementation does not support blink feature for
GPLEDs. Blink functionality is required if user wants to
produce fading effects using GPLEDs. Hence, adding blink
functionality to GPLEDs.

Change-Id: I87886469b05cf75986e89ebc3f28d9a6a386401f
Signed-off-by: Abinaya P <abinayap@codeaurora.org>