mmc, sh: Move constants to sh_mmcif.h

This moves some constants from sh_mmcif.c to sh_mmcif.h
so that they can be used in sh_mmcif_boot_init().

It also alters the definition of SOFT_RST_OFF from (0 << 31) to
~SOFT_RST_ON (= ~(1 << 31)). The former seems bogus.  The latter is
consistent with the code in sh_mmcif_boot_init().

Cc: Yusuke Goda <yusuke.goda.sx@renesas.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>