drm/amdgpu: Define one variable for virtual display.

For virtual display feature, define on variable in amdgpu.ko. When want to
enable virtual display feature, need set the option "amdgpu.virtual_display=1".
And then disable vga render and crtc if have DCE engine.
Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -92,6 +92,7 @@ extern unsigned amdgpu_cg_mask;
 extern unsigned amdgpu_pg_mask;
 extern char *amdgpu_disable_cu;
 extern int amdgpu_sclk_deep_sleep_en;
+extern int amdgpu_virtual_display;
 
 #define AMDGPU_WAIT_IDLE_TIMEOUT_IN_MS	        3000
 #define AMDGPU_MAX_USEC_TIMEOUT			100000	/* 100 ms */

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

@@ -90,6 +90,7 @@ unsigned amdgpu_pcie_lane_cap = 0;
 unsigned amdgpu_cg_mask = 0xffffffff;
 unsigned amdgpu_pg_mask = 0xffffffff;
 char *amdgpu_disable_cu = NULL;
+int amdgpu_virtual_display = 0;
 
 MODULE_PARM_DESC(vramlimit, "Restrict VRAM for testing, in megabytes");
 module_param_named(vramlimit, amdgpu_vram_limit, int, 0600);
@@ -189,6 +190,9 @@ module_param_named(pg_mask, amdgpu_pg_mask, uint, 0444);
 MODULE_PARM_DESC(disable_cu, "Disable CUs (se.sh.cu,...)");
 module_param_named(disable_cu, amdgpu_disable_cu, charp, 0444);
 
+MODULE_PARM_DESC(virtual_display, "enable virtual display (0 = disable virtual display)");
+module_param_named(virtual_display, amdgpu_virtual_display, int, 0444);
+
 static const struct pci_device_id pciidlist[] = {
 #ifdef CONFIG_DRM_AMDGPU_CIK
 	/* Kaveri */