At least on some NVIDIA cards the default scaling mode makes
black borders visible on all sides, even on native resolution.
This patch adds a generic "scaling MODE" command to vgactl
and adds support for it on VESA through NVIDIA VBE OEM extension.
It hasn't been tested on any other video cards, but shouldn't
break anything as the scaling mode is only set on write to vgactl.
allow the shadow framebuffer (softscreen) to be used with any
vga driver, not just vesa. this removes the ugly scr->paddr = 0
hack employed by vesa driver to force softscreen and adds a
softscreen vgactl message that can switch the feature on and off
at runtime.
softscreen can greatly improve graphics performance when bus
reads are slow even tho it disables hardware acceleration.
