Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

MFP4 change 219820

Add a missing 0 to the mask for byte0 of C_SIZE.

The previous mask (0xc) worked except that the last 0-1536K of the disk
could not be accessed since we were shifting the (wrong) bits we did
mask off the right edge.

Merge Perforce changeset 219952 to head:

Make different bus attachments for Altera and Terasice
device drivers share the same devclass_t.

Sponsored by: DARPA, AFRL

Add a device driver for the Altera University Program SD Card IP Core,
which can be synthesised in Altera FPGAs. An altera_sdcardc device
probes during the boot, and /dev/altera_sdcard devices come and go as
inserted and removed. The device driver attaches directly to the
Nexus, as is common for system-on-chip device drivers.

This IP core suffers a number of significant limitations, including a
lack of interrupt-driven I/O -- we must implement timer-driven polling,
only CSD 0 cards (up to 2G) are supported, there are serious memory
access issues that require the driver to verify writes to memory-mapped
buffers, undocumented alignment requirements, and erroneous error
returns. The driver must therefore work quite hard, despite a fairly
simple hardware-software interface. The IP core also supports at most
one outstanding I/O at a time, so is not a speed demon.

However, with the above workarounds, and subject to performance
problems, it works quite reliably in practice, and we can use it for
read-write mounts of root file systems, etc.

Sponsored by: DARPA, AFRL