drm/i915: Remove the broken DP CRC support for g4x

drm/i915: Remove the broken DP CRC support for g4x

DP CRCs don't really work on g4x. If you want any CRCs on DP you must
select the CRC source before the port is enabled, otherwise the CRC
source select bits simply ignore any writes to them. And once the port
is enabled we mustn't change the CRC source select until the port is
disabled. That almost works, but not quite :( Eventually the CRC source
select bits get permanently stuck one way or the other, and after that
a reboot (or possibly a display reset) is needed to get working CRCs
on that pipe (not matter which CRC source we try to use).

Additionally the DFT scrambler reset bits we're trying to use don't
seem to exist on g4x. There are some potentially relevant looking bits
in the pipe registers, but when I tried it I got stable looking CRCs
without setting any bits for this.

If there is a way to make DP CRCs work reliably on g4x, I wasn't
able to find it. So let's just remove the broken code we have.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190214192219.3858-3-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>