drm/i915: Make intel_dp_process_phy_request() static

intel_dp_process_phy_request() has no business being externally
visible. Make it static.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200929233449.32323-4-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>