drm/i915/pps: rename vlv_init_panel_power_sequencer to vlv_pps_init

This function is a bit of an outlier, but try to change to a name that
is more in line with the rest of the intel_pps 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/644b89c1d88d4d2cd7a9426ec7d7ea14eb65a8bc.1610127741.git.jani.nikula@intel.com