leds: qpnp-wled: Add support to configure AUTO_GM settings

WLED in pmicobalt supports AUTO_GM configuration in CTRL_VLOOP_COMP_GM
register. Add two properties to enable auto-gm and set auto-gm threshold.
Meanwhile, move "qcom,loop-ea-gm" property outside of AMOLED constraint
because WLED in LCD mode also support it.

CRs-Fixed: 1081738
Change-Id: Iee99e9d1b999c84ece075d2f17e9cdf6aef9a2ac
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>