drm/amd/display: Disable GSL when enabling phantom pipe

[Description]
When enabling phantom pipe on a pipe that was previously
using immediate flip, we have to disable GSL or this will
prevent the update from taking place right away on the phantom
pipe when we enable it in FW
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn32/dcn32_hubp.c

@@ -79,6 +79,8 @@ void hubp32_phantom_hubp_post_enable(struct hubp *hubp)
 	uint32_t reg_val;
 	struct dcn20_hubp *hubp2 = TO_DCN20_HUBP(hubp);
 
+	/* For phantom pipe enable, disable GSL */
+	REG_UPDATE(DCSURF_FLIP_CONTROL2, SURFACE_GSL_ENABLE, 0);
 	REG_UPDATE(DCHUBP_CNTL, HUBP_BLANK_EN, 1);
 	reg_val = REG_READ(DCHUBP_CNTL);
 	if (reg_val) {