sh: LCDC start_transfer() for the KFR2R09 board

This patch adds a ->start_transfer() callback to the
KFR2R09 lcd handling code. The callback is used to
notify the lcd controller that a new frame of data
is about to be transferred. The callback is only used
in combination with deferred io, but the code has
been tested both with and without deferred io enabled.

Without this patch the display data on the KFR2R09
lcd panel becomes corrupted over time.

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