drm/i915/dp: rename intel_dp_is_edp to intel_dp_is_port_edp

drm/i915/dp: rename intel_dp_is_edp to intel_dp_is_port_edp

Emphasize that this is based on the port, not intel_dp. This is also in
line with the underlying intel_bios_is_port_edp() function. No
functional changes.

Cc: Manasi Navare <[email protected]>
Cc: Jim Bride <[email protected]>
Reviewed-by: Jim Bride <[email protected]>
Reviewed-by: Manasi Navare <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]