drm/i915/dp: there is no audio on port A

drm/i915/dp: there is no audio on port A

commit 9fcb1704d1d51b12e2f03c78bca013d0cbbb7c98 upstream.

The eDP port A register on PCH split platforms has a slightly different
register layout from the other ports, with bit 6 being either alternate
scrambler reset or reserved, depending on the generation. Our
misinterpretation of the bit as audio has lead to warning.

Fix this by not enabling audio on port A, since none of our platforms
support audio on port A anyway.

v2: DDI doesn't have audio on port A either (Sivakumar Thulasimani)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89958
Reported-and-tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>