mmc: tmio-mmc: add support for 32bit data port

For the r7s72100 SOC, the DATA_PORT register was changed to 32-bits wide.
Therefore a new flag has been created that will allow 32-bit reads/writes
to the DATA_PORT register instead of 16-bit (because 16-bits accesses are
not supported).

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>