leds: qpnp-wled: Fix configuration of avdd_trim registers

Currently the avdd_trim registers are being configured incorrectly.
Update the sequence to configure the trim register and the OVP
register based on predetermined values mapped to the target voltage
specified in the device tree. Also add support for performing
masked writes to the wled registers.

CRs-Fixed: 1010716
Change-Id: I4c99b598d5f484368712eab239f7de70b727c2aa
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>