drm/i915/dsi: rename intel_dsi_panel_vbt.c to intel_dsi_vbt.c

Emphasize that the VBT file is nowadays more about initializing and
running stuff based on the VBT contents, not so much about being a
"panel driver". No functional changes.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Cc: Madhav Chauhan <madhav.chauhan@intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/b13cb012a555ff5eb56b5e4bb2b0205c3e025a99.1488810382.git.jani.nikula@intel.com