sunxi: video: Prepare for lcd support

Refactor sunxi_mode_set into a bunch of helpers, and make it do a switch
case on sunxi_display.monitor to decide what to do.

Also rename sunxi_lcdc_mode_set to sunxi_lcdc_tcon1_mode_set, as it sets the
timings for tcon1, and for lcd support we need a similar function operating
on tcon0.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>