[mucurses] Use "<ESC>[2J" ANSI escape sequence to clear screen

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[console] Allow console input and output to be disabled independently

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[console] Add concept of generic console configuration

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[cmdline] Add "console" command to configure console

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[fbcon] Add generic concept of a frame buffer console

Add support for a simple frame buffer console, using single buffering
and a fixed-width bitmap font.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[vesafb] Add VESA frame buffer console

The VESA frame buffer console uses the VESA BIOS extensions (VBE) to
enumerate video modes, selects an appropriate mode, and then hands off
to the generic frame buffer code.

The font is extracted from the VGA BIOS, avoiding the need to provide
an external font file.

Signed-off-by: Michael Brown <mcb30@ipxe.org>