ARM: dts: msm: specify DSI panel regulators in panel dtsi node

Regulators that are needed to supply power to the panel are currently
specified in the DSI controller dtsi node. This limits the support of
multiple panels on a single software build, since every panel may have
a different set of regulator supply configurations. Hence, add the driver
support to specify the panel regulators in panel dtsi file instead
of mdss dtsi file and update the panel dtsi files accordingly.

Change-Id: Icd512f0bcc353d4e856b9dbe5dead5a108f1318b
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>