disp: msm: support framebuffer emulation in KMS driver

framebuffer support is required in some use cases, so add
framebuffer emulation for KMS driver.

Change-Id: Icf0bbcd59ca430478d2bef4df033988d0338f2bb
Signed-off-by: Ray Zhang <rayz@codeaurora.org>

msm/sde/sde_kms.c

@@ -2944,6 +2944,8 @@ static int _sde_kms_mmu_init(struct sde_kms *sde_kms)
 		}
 	}
 
+	sde_kms->base.aspace = sde_kms->aspace[0];
+
 	return 0;
 
 early_map_fail: