drm/i915/pps: rename intel_dp_check_edp to intel_pps_check_power_unlocked

Follow the usual naming pattern for functions. No functional changes.

Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f03f7195fb62b250847909e0972f69a151095529.1610127741.git.jani.nikula@intel.com