msm: mdss: add 5v-boost-gpio to dsi panel node

Certain DSI panels need 5v boost gpio to be configured
to work. Add support to define and enable 5v boost gpio as a
panel property. These panels in older targets were relying on
the platform enable gpio to enable the 5v boost on the panel.
This maintains back compatibility for those targets which use
the same panels.

Change-Id: I0410a83044e17648e67a9e8556c5620c75472e62
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>