drm/i915/dsi: update reset and power sequences in panel prepare/unprepare hooks

Based on the documentation alone, it's anyone's guess when exactly we
should be running these sequences. Add power on/off sequences where they
feel logical and update assert/deassert reset. The drm panel hooks don't
currently offer us more granularity anyway.

v2: update assert/deassert reset as well (Ville)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1543320494df953fa073e136248238eaa1eed059.1474286487.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_dsi_panel_vbt.c

@@ -459,6 +459,8 @@ static void generic_exec_sequence(struct drm_panel *panel, enum mipi_seq seq_id)
 static int vbt_panel_prepare(struct drm_panel *panel)
 {
 	generic_exec_sequence(panel, MIPI_SEQ_ASSERT_RESET);
+	generic_exec_sequence(panel, MIPI_SEQ_POWER_ON);
+	generic_exec_sequence(panel, MIPI_SEQ_DEASSERT_RESET);
 	generic_exec_sequence(panel, MIPI_SEQ_INIT_OTP);
 
 	return 0;
@@ -466,7 +468,8 @@ static int vbt_panel_prepare(struct drm_panel *panel)
 
 static int vbt_panel_unprepare(struct drm_panel *panel)
 {
-	generic_exec_sequence(panel, MIPI_SEQ_DEASSERT_RESET);
+	generic_exec_sequence(panel, MIPI_SEQ_ASSERT_RESET);
+	generic_exec_sequence(panel, MIPI_SEQ_POWER_OFF);
 
 	return 0;
 }