Adjust the tmio_mmc block size check to accept 2-byte requests in 4-bit
mode if the hardware supports it.

Tested with the SDHI hardware block included in sh7724.
Signed-off-by: NYusuke Goda <yusuke.goda.sx@renesas.com>
Signed-off-by: NMatt Fleming <matt@console-pimps.org>
Acked-by: NMagnus Damm <damm@opensource.se>
Tested-by: NArnd Hannemann <arnd@arndnet.de>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>