drm: add LG eDP panel to quirk database

The N value was computed by kernel driver that based on synchronous clock
mode. But only specific N value (0x8000) would be acceptable for
LG LP140WF6-SPM1 eDP panel which is running at asynchronous clock mode.
With the other N value, Tcon will enter BITS mode and display black screen.
Add this panel into quirk database and give particular N value when
calculate M/N divider.

v2: no update
v3: add lost commit messages back for version 2
v4: send patch to both intel-gfx and dri-devel

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Lee, Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1536733371-25004-4-git-send-email-shawn.c.lee@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -1271,6 +1271,8 @@ struct dpcd_quirk {
 static const struct dpcd_quirk dpcd_quirk_list[] = {
 	/* Analogix 7737 needs reduced M and N at HBR2 link rates */
 	{ OUI(0x00, 0x22, 0xb9), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_CONSTANT_N) },
+	/* LG LP140WF6-SPM1 eDP panel */
+	{ OUI(0x00, 0x22, 0xb9), DEVICE_ID('s', 'i', 'v', 'a', 'r', 'T'), false, BIT(DP_DPCD_QUIRK_CONSTANT_N) },
 };
 
 #undef OUI