Prepare support to be able to handle font data in loader, consolidate
data structures to sys/font.h and update vtfontcvt.
vtfontcvt update is about to output set of glyphs in form of C source,
the implementation does allow to output compressed or uncompressed font
bitmaps.
Reviewed by: bcr
Differential Revision: https://reviews.freebsd.org/D24189
vtfontcvt is useful for end users to convert arbitrary bitmap fonts
for use by vt(4). It can also be used as a build tool, allowing us
to keep the source font data in the src tree rather than uuencoded
binaries.
Reviewed by: ray, wblock (D183)
Sponsored by: The FreeBSD Foundation
