drm/i915/dp: Include the time taken by AUX Tx for timeout

drm/i915/dp: Include the time taken by AUX Tx for timeout

As per DP spec the timeout for LANE_CHANNEL_EQ_DONE is 400ms. But this
timeout value is exclusively for the Aux RD Interval and excludes the
time consumed for the AUX Tx (i.e reading/writing FFE presets). Add
another 50ms for these AUX Tx to the 400ms timeout.
Ref: "Figure 3-52: 128b132b DP DPTC LANEx_CHANNEL_EQ_DONE Sequence" of
DP2.1a spec.

Co-developed-by: Srikanth V NagaVenkata <nagavenkata.srikanth.v@intel.com>
Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240925034432.1777029-4-arun.r.murthy@intel.com