drm/i2c: nxp-tda998x (v3)

Driver for the NXP TDA998X i2c hdmi encoder slave.

v1: original
v2: fix npix/nline programming
v3: add Kconfig, fix dup'd MODULE_DESCRIPTION

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Koen Kooi <koen@dominion.thruhere.net>