amdgpu: Fix wrappers for AMDGPU_VM IOCTL.

Rmove amdgpu_context_handle from the interface and use
amdgpu_device_handle instead. Uupdate VMID reservation test
accordingly.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>