drm/amdgpu: Remove duplicate amdgpu_umsch_mm.h header

./drivers/gpu/drm/amd/amdgpu/amdgpu.h: amdgpu_umsch_mm.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9063


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>