amdkfd: Remove DRM_AMDGPU dependency from Kconfig

This patch removes the dependency of amdkfd upon DRM_AMDGPU symbol in amdkfd's
Kconfig file.

This is done because amdgpu driver is not yet upstreamed and therefore,
DRM_AMDGPU symbol is not present in any Kconfig file.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>