leds: qcom-clk: Add support to set default trigger for LED

Add property to configure the default trigger for the LED.
This will allow clients to use trigger APIs to configure
the brightness of the LED if needed.

Change-Id: I1db0a5f2d697c6ac6f6ae1296e43ae55509f2298
Signed-off-by: Veera Vegivada <vvegivad@codeaurora.org>