Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

All SD cards have a block size of 512. The READ_BL_LEN field in the
CSD is usually 512 (well, 9), but for 2GB (and the rogue 4GB SD cards)
it is 1024 (or 2048 for 4GB). This value doesn't work for the block
read commands (which really want 512). Hardcode 512 for those. This
may break really old MMC cards that don't have a 512 block size (I've
never seen one: make my day and send me one :-), but since the MMC
side of the house is currently broken, it should only have the effect
that 2GB (and non-conforming 4GB) SD cards will work.

My 'non-conforming' 4GB SD card also works now too. The
non-conforming 4GB SD cards were sold for a while before the SD
association was worried they would be (a) incompatible (different FAT
flavor on them) and (b) confusing for the new SDHC standard and
cracked down on suppliers' bogus use of the SD trademark...

MFp4: boot on KB9202 correctly. Also, reduce the size of the SD/MMC driver
somewhat.

MFp4:

Massive update. The highlights:
o dramatically cut memory usage by writing better, less intertwingled
code.
o implement booting off mmc/sd cards (sd only tested one at the moment)
o start to split out board specific stuff for boot2.

MFp4: First cut at making spi and/or sd card booting work, needs work