leds: qpnp-flash-v2: Add support for configuring OTST thresholds

Add support for configuring the three thermal mitigation
thresholds from device tree.

CRs-Fixed: 1060212
Change-Id: Iafb7915e196a18b5f8076dda8fb06a4bd71a8e6e
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>