drm/amdgpu/userq: add UAPI for setting queue priority

Allow the user to set a queue priority levels:
0 - normal low - most apps (maps to MES AMD_PRIORITY_LEVEL_NORMAL)
1 - low - background jobs (maps to MES AMD_PRIORITY_LEVEL_LOW)
2 - normal high - apps that need relative high (maps to MES AMD_PRIORITY_LEVEL_MEDIUM)
3 - high (admin only - for compositors) (maps to MES AMD_PRIORITY_LEVEL_HIGH)

Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Jesse.Zhang <Jesse.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>