This patch adds r8a7793 GOSE HDMI video out support.

The r8a7793 GOSE board is similar to r8a7791 Koelsch. For those
boards an on-board HDMI encoder chip provides HDMI video out
and also a LVDS port is available for external LCD panels.

Tested on r8a7793 Gose with HDMI hooked up to a Toshiba TV.
Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
[simon: rebased; reused existing i2c2 node]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>