drm/radeon: Always flush the VM

drm/radeon: Always flush the VM

commit 466476dfdcafbb4286ffa232a3a792731b9dc852 upstream.

This is slightly cleaned up version of Jerome's patch.
There seems to be an issue tracking the last flush of
the VM which results in hangs in certain cases when
VM is used.  For now just flush the VM for every IB.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=62959
https://bugs.freedesktop.org/show_bug.cgi?id=62997

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>