leds: qpnp-wled: add support to control PSM dynamically

As per the hardware recommendation, keep PSM disabled 10 ms after
WLED module is enabled. Enable PSM back when the module is
disabled. This is to ensure that PFM mode is operational without
the precedence from PSM. Make this configurable through a device
tree property.

Change-Id: Ic6be160a88be40e94a4a0798646b8aa3f169ab49
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>