mmc: sh_mmcif: revision-specific Command Completion Signal handling

Some earlier MMCIF IP revisions contained Command Completion Signal
support, which has been dropped again in modern versions. Sopport for
this feature is added in a way to preserve the current behaviour by
default, i.e. when it is not enabled in platform data. Patch is based
on work by Nobuyuki HIRAI.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>