Implement long-since-promised video functions defined in
<syslinux/video.h>.  Use these functions in initvesa.c instead of
open-coding the same functionality.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Don't display the cursor on the graphical screen while doing a quiet
boot.  When doing a quiet boot we will probably show the graphical
screen for a fair bit of time; as a result, we really don't want a
completely bogus cursor blob on the bottom of the screen.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Make it possible to request nonstandard resolutions when enabling
vesacon.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Impact: avoid code duplication

This will make code more generic, hdt will need it ;)

Impact: sync with linux kernel

cpu flags are now in sync with the linux kernel. Too many flags were
missing.

Fix an uninitialized pointer bug; return void rather than returning
int like normal printfs... if we're depending on the return value of a
debugging function we're screwed when debugging is disabled.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Actually provide real infrastructure for debug-to-serial.  Very
useful when debugging fullscreen applications, especially under an
emulator like Qemu.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

There was a bug in HDT when switching from the menu to the cli and
back to the menu: the background wasn't redrawn.

This was due to the fact that the cli bypasses the libansi library
and calls printf() directly. Unfortunately, the SGR attributes were
cached between menu initializations and the background wasn't properly
redrawn.

To fix it, invalidate the cache in the cls() routine. cls() does much
more than just erasing the screen already (e.g. initialize G1) - we
may want to rename the function at some point.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>