[POWERPC] spufs: wrap mfc sdr access

SPRN_SDR1 and the SPE's MFC SDR are hypervisor resources and
are not accessible from a logical partition.  This change adds an
access wrapper.

When running on bare H/W, the spufs needs to only set the SPE's MFC SDR
to the value of the PPE's SPRN_SDR1 once at SPE initialization, so this
change renames mfc_sdr_set() to mfc_sdr_setup() and moves the
access of SPRN_SDR1 into the mmio wrapper.  It also removes the now
unneeded member mfc_sdr_RW from struct spu_priv1_collapsed.

Signed-off-by: Masato Noguchi <Masato.Noguchi@jp.sony.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

--
Signed-off-by: Paul Mackerras <paulus@samba.org>