msm: mdss: Add support for dynamic mode switch

Add support for switching between dsi command mode and
video mode and vice versa at runtime. If the panel is
configured in video mode, it would be power efficient to
be able to dynamically switch to command mode on need
basis. This change adds the support by providing an IOCTL
to switch between video mode and command mode at runtime.

Change-Id: I573c063556d68d631fe27cc2d1447522eceb7f2a
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>