tcx: Implement hardware acceleration

The S24/TCX framebuffer is a mildly accelerated video card with
blitter, stippler and hardware cursor.

* Solaris and NetBSD 6.x use all the hardware acceleration features
* The Xorg driver (used by Linux) can use the hardware cursor only

This patch implements hardware acceleration in both 8 bit and 24 bit
modes. It is based on the NetBSD driver sources and from tests with
Solaris.

Signed-off-by: Olivier Danet <odanet@caramail.com>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>