- Verify that we don't load more data into a FIFO than it is
configured to handle.
- Add code to handle suspend and resume.

MFC after:	3 days
Support "GNU Unifont" format font data

The GNU Unifont .hex format is a text file.  Each line represents one
glyph and consists of a four-digit hex code point, a colon, and pairs of
hex digits representing the bitmap.  By default an 8x16 font is assumed,
with 16x16 double-width glyphs, resulting in either 32 or 64 hex digits
for the bitmap.

Our version of the file format supports comments at the top of the file
to set the height and width:

# Height: <decimal height>
# Width: <decimal width>

Each row of bitmap data is rounded up to byte width - for example, a
10-pixel wide font uses 4 characters per row.

See http://czyborra.com/unifont/ for more background on the original
format.

Sponsored by:	The FreeBSD Foundation