aw_mmc: Reset controller and configure read fifo size

[thj]

Summary

On h616 (and I think h6, but this isn't verified) we need to reset the
controller, configure read and write and set the read fifo size to get a
working sd card.

[adrian]

This looks fine to me, nice catch!

[manu]

sys/arm/allwinner/aw_mmc.c

746

How where those delay chosen and why it's only done where there is a fifo threashold ?

752

We disable the FIFO and never use it so are you sure that it's needed ?

[thj]

remove fifo configuration and delays

[thj]

remove sleeps