ARM: dts: msm: add the LAB/IBB regulator nodes to panel dtsi

Currently, the LAB/IBB regulators to supply power to the panel are
controlled in MDSS DSI drivers and the property to enable it is part
of MDSS DSI node. This needs to be ideally enabled/controlled through
the panel dtsi. Add support to control these regulators similar to
the other PMIC LDO regulators via the panel dtsi node for 8994, 8992,
8996 and 8952. Cleanup the existing code in DSI drivers related to
LAB/IBB control.

Change-Id: Ie504da64f7752625060717dbeb08f8da1c87c98e
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>