drm/amdgpu: there is no vbios fb on devices with no display hw (v2)

If we enable virtual display functionality on parts with
no display hardware we can end up trying to check for and
reserve the vbios FB area on devices where it doesn't exist.
Check if display hardware is actually present on the hardware
before trying to reserve the memory.

v2: move the check into common code

Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1298,6 +1298,7 @@ void amdgpu_device_pcie_port_wreg(struct amdgpu_device *adev,
 				u32 reg, u32 v);
 struct dma_fence *amdgpu_device_switch_gang(struct amdgpu_device *adev,
 					    struct dma_fence *gang);
+bool amdgpu_device_has_display_hardware(struct amdgpu_device *adev);
 
 /* atpx handler */
 #if defined(CONFIG_VGA_SWITCHEROO)