mmc: renesas_sdhi: limit block count to 16 bit for old revisions

R-Car Gen2 has two different SDHI incarnations in the same chip. The
older one does not support the recently introduced 32 bit register
access to the block count register. Make sure we use this feature only
after the first known version.

Thanks to the Renesas Testing team for this bug report!

Fixes: 5603731a ("mmc: tmio: fix access width of Block Count Register")
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Tested-by: Phong Hoang <phong.hoang.wz@renesas.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>