drm/i915/display: Don't disable DDI/Transcoder when setting phy test pattern

Bspecs has updated recently to remove the restriction to disable
DDI/Transcoder before setting PHY test pattern. This update is to
address PHY compliance test failures observed on a port with LTTPR.
The issue is that when Transc. is disabled, the main link signals fed
to LTTPR will be dropped invalidating link training, which will affect
the quality of the phy test pattern when the transcoder is enabled again.

v2: Update commit message (Clint)
v3: Add missing Signed-off in v2
v4: Update Bspec and commit message for pre-gen12 (Jani)

Bspec: 50482, 7555
Fixes: 8cdf7271 ("drm/i915/dp: Program vswing, pre-emphasis, test-pattern")
Cc: Imre Deak <imre.deak@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
CC: Jani Nikula <jani.nikula@intel.com>
Tested-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Reviewed-by: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221123220926.170034-1-khaled.almahallawy@intel.com