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

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

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 terasic_mtl(4), a device driver for the Terasic Multi-Touch LCD,
used with Terasic's DE-4 and other similar FPGA boards. This display
is 800x480 and includes a capacitive touch screen, multi-touch
gesture recognition, etc. This device driver depends on a Cambridge-
provided IP core that allows the MTL device to be hooked up to the
Altera Avalon SoC bus, and also provides a VGA-like text frame buffer.

Although it is compiled as a single device driver, it actually
implements a number of different device nodes exporting various
aspects of this multi-function device to userspace:

- Simple memory-mapped driver for the MTL 24-bit pixel frame buffer.
- Simple memory-mapped driver for the MTL control register set.
- Simple memory-mapped driver for the MTL text frame buffer.
- syscons attachment for the MTL text frame buffer.

This driver attaches directly to Nexus as is common for SoC device
drivers, and for the time being is considered BERI-specific, although
in principle it might be used with other hard and soft cores on
Altera FPGAs.

Control registers, including touchscreen input, are simply memory
mapped; in the future it would be desirable to hook up a more
conventional device node that can stream events, support kqueue(2)/
poll(2)/select(2), etc.

This is the first use of syscons on MIPS, as far as I can tell, and
there are some loose ends, such as an inability to use the hardware
cursor. More fundamentally, it appears that syscons(4) assumes that
either a host is PC-like (i386, amd64) *or* it must be using a
graphical frame buffer. While the MTL supports a graphical frame
buffer, using the text frame buffer is preferable for console use.
Fixing this issue in syscons(4) requires non-trivial changes, as the
text frame buffer support assumes that direct memory access can be
done to the text frame buffer without using bus accessor methods,
which is not the case on MIPS. As a workaround for this, we instead
double-buffer and pretend to be a graphical frame buffer exposing
text accessor methods, leading to some quirks in syscons behaviour.

Sponsored by: DARPA, AFRL