fbset: add possibility to set timing and sync polarity

fbset: add possibility to set timing and sync polarity

function                                             old     new   delta
copy_changed_values                                    -      48     +48
copy_if_gt0                                            -      27     +27
fbset_main                                          1268    1235     -33
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 0/1 up/down: 75/-33)             Total: 42 bytes

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>