fbdev: sh_mipi_dsi: Allow LCDC board callbacks

Update the MIPI-DSI driver to make use of the
LCD panel callbacks in the LCDC platform data.

Without this patch MIPI panels cannot use board
specific LCDC callbacks to control power and/or
back light.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>