parisc/sticon: Add user font support

This is a major rework of the sticon (parisc text console) driver in
order to support user font support.

Usually one want to use the stifb (parisc framebuffer driver) which is
based on fbcon and does support fonts and colors, but some old machines
(e.g. HP 730 workstations) don't provide a supported stifb graphic card,
and for those user fonts are preferred.

This patch drops unused code for software cursor and scrollback,
enhances the debug output and adds better documentation.

The code was tested on various machines with byte-mode and word-mode
graphic cards on GSC- and PCI-busses.

Signed-off-by: Helge Deller <deller@gmx.de>