leds: qpnp-flash-v2: Add support to handle ramp up and down irqs

Add support to register and handle the all-ramp-up-done
and all-ramp-down-done irqs for flash-led.

CRs-Fixed: 921325
Change-Id: I843a008dbe6900f9f16c202a05435dbaf7a37627
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>