vgabios: Support custom fonts in vga framebuffer text writing.

Obtain the font data from int 0x43 and int 0x1f, and obtain the font
height from the BDA.  This enables application overrides for the font
data.

This patch also unifies the variable naming between the
planar/CGA/linear character writing functions and uses the same names
that the screen scrolling functions use.

This patch also optimizes the inner loop of the CGA font writing to
reduce overall stack usage.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
vgabios: Add bochsvga "HDTV" resolutions.

The same set of video modes were added to the "lgpl vgabios" in
release 0.7a.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
vgabios: Avoid possible divide by zero in bochsvga_set_displaystart.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
vgabios: Work around lack of support for "calll" in x86emu emulation.

Replace 32 bit call instructions with 16 bit call instructions in the
vgabios to workaround problems in old versions of x86emu.  This change
allows fc13 and fc14 to boot.  (Other x86emu emulation bugs still
prevent fc11 and fc12 from booting.)

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Minor - update file comment on bootsplash.c.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>