drm/amdgpu: Enable gfxoff quirk on MacBook Pro

Enabling gfxoff quirk results in perfectly usable graphical user
interface on MacBook Pro (15-inch, 2019) with Radeon Pro Vega 20 4 GB.

Without the quirk, X server is completely unusable as every few seconds
there is gpu reset due to ring gfx timeout.

Signed-off-by: Tomasz Moń <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c

···
 	{ 0x1002, 0x15dd, 0x103c, 0x83e7, 0xd3 },
 	/* GFXOFF is unstable on C6 parts with a VBIOS 113-RAVEN-114 */
 	{ 0x1002, 0x15dd, 0x1002, 0x15dd, 0xc6 },
+	/* Apple MacBook Pro (15-inch, 2019) Radeon Pro Vega 20 4 GB */
+	{ 0x1002, 0x69af, 0x106b, 0x019a, 0xc0 },
 	{ 0, 0, 0, 0, 0 },
 };