[MMC] Convert all hosts except mmci to use data->blksz

The MMC specification allows non-power of two block sizes.  As such,
we should not pass the log2 block size to host drivers, but instead
pass the byte size.

However, ARM MMCI can only work with log2 block size, so continue to
pass both the log2 block size and byte block size.  This means that
for the moment, the byte block size must remain a power of two, but
this is the first stage of removing this restriction for other hosts.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>