drm/amdgpu: Basic emulation support

Add amdgpu_emu_mode module parameter to control the emulation mode
Avoid vbios operation on emulation since there is no vbios post duirng emulation,
use the common hw_init to simulate the post

Signed-off-by: Shaoyun Liu <Shaoyun.Liu@amd.com>
Acked-By: Alex Deucher <alexander.deucher@amd.com>
Acked-By: Christian Konig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -128,6 +128,7 @@ extern int amdgpu_job_hang_limit;
 extern int amdgpu_lbpw;
 extern int amdgpu_compute_multipipe;
 extern int amdgpu_gpu_recovery;
+extern int amdgpu_emu_mode;
 
 #ifdef CONFIG_DRM_AMDGPU_SI
 extern int amdgpu_si_support;