Partial rewrite of SDHOST driver to use DMA for data transfer

This reverts the microSD performance to that seen with the SDHCI controller.

Benchmarks on Pi Zero W (ARM1176JZF-S):
  SDHCI:      23.8 MB/s
  SDHOST PIO:  1.9 MB/s
  SDHOST DMA: 24.4 MB/s

Benchmarks on Pi Zero 2W (Cortex-A53):
  SDHCI:      23.8 MB/s
  SDHOST PIO:  8.6 MB/s
  SDHOST DMA: 24.4 MB/s
10 jobs for !20 with SDIO in 8 seconds (queued for 25 seconds)
detached
Status Job ID Name Coverage
  Static Analysis
passed #42635
cross
gitattributes

00:00:00

passed #42636
cross
gitignore

00:00:00

passed #42639
cross
head_log

00:00:00

passed #42642
cross
head_whitesp

00:00:00

passed #42637
cross
license

00:00:00

passed #42641
cross
makefile

00:00:00

passed #42640
cross
merge_log

00:00:01

passed #42643
cross
merge_whitesp

00:00:01

passed #42638
cross
versionnum

00:00:00

 
  Cleanup
passed #42644
cross
cleanup

00:00:00