leds:qpnp-flash-v2: Add support for flash realtime control

In the default design, every time we change the brightness
in torch node it gets reflected only when the enable bit
in the switch node is toggled from 0 to 1. Add new DT property
to optionally allow brightness change to reflect in realtime,
for as long as the switch node enable bit remains set.

Change-Id: I0bc339ba2488177fff144b2771e9a8db425ced84
Signed-off-by: Kavya Nunna <quic_knunna@quicinc.com>