drm/edid: Add 6 bpc quirk for SDC panel in Lenovo G50

Another panel that needs 6BPC quirk.

BugLink: https://bugs.launchpad.net/bugs/1819968
Cc: <stable@vger.kernel.org> # v4.8+
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190402033037.21877-1-kai.heng.feng@canonical.com