drm/amdgpu: Change the virtual_display type from int to char*.

For virtual display feature, as there may be multiple GPUs,
for user could choose whiche GPU need to enable this feature, change
the type of virtual_display from int to char*. The variable will be set
like this virtual_display="xxxx:xx:xx.x;xxxx:xx:xx.x;".

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>
diff --git a/drivers/gpu/drm/amd/amdgpu/vi.c b/drivers/gpu/drm/amd/amdgpu/vi.c
index 69c2f81..f2e8aa1 100644
--- a/drivers/gpu/drm/amd/amdgpu/vi.c
+++ b/drivers/gpu/drm/amd/amdgpu/vi.c
@@ -1441,7 +1441,7 @@
 
 int vi_set_ip_blocks(struct amdgpu_device *adev)
 {
-	if (amdgpu_virtual_display) {
+	if (adev->enable_virtual_display) {
 		switch (adev->asic_type) {
 		case CHIP_TOPAZ:
 			adev->ip_blocks = topaz_ip_blocks_vd;