Per datasheet: maximum block length is 2048 bytes,
data length field is in bits 0-23 of the Data Length Register.

Also for DMA mode we have to take into account rx/tx buffers' sizes.

In my tests this change doubles SD card I/O performance on big files.
Before the change Linux used default request size of 4 KB.
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Link: https://lore.kernel.org/r/20230210143843.369943-1-saproj@gmail.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>