media: platform: amd: add DRM_AMDGPU dependency

media: platform: amd: add DRM_AMDGPU dependency

With DRM_AMDGPU=m and DRM_AMD_ISP=y, it is possible to configura
VIDEO_AMD_ISP4_CAPTURE as built-in, but that fails to link:

aarch64-linux-ld: drivers/media/platform/amd/isp4/isp4_interface.o: in function `isp4if_gpu_mem_alloc.isra.0':
isp4_interface.c:(.text+0x1d0): undefined reference to `isp_kernel_buffer_alloc'
aarch64-linux-ld: drivers/media/platform/amd/isp4/isp4_interface.o: in function `isp4if_dealloc_fw_gpumem':
isp4_interface.c:(.text+0x26c): undefined reference to `isp_kernel_buffer_free'

Add a dependency on the tristate DRM_AMDGPU symbol in addition to
the boolean DRM_AMD_ISP=y, so this can only be built-in if
the ISP driver is also linked into the kernel itself.

Fixes: 9a54c285630c ("media: platform: amd: Introduce amd isp4 capture driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Bin Du <Bin.Du@amd.com>
Tested-by: Bin Du <Bin.Du@amd.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>