leds: qcom-clk: Add clock controller based PWM driver

Duty cycle of the clock can be controlled by D register of the RCG.
Add support for configuring the duty cyles through LED framework's
brightness. Pinctrl settings are needed for configuring the pins to
output the core clock on the pin.

Change-Id: Id2dd3ef34943c07731e27ca8b7e1d04d1b8e231e
Signed-off-by: Veera Vegivada <vvegivad@codeaurora.org>