Instead of cowboy-calling the VESA BIOS in the bootloader, find the emulator
VGA adapter by scanning the PCI bus. Then set up the desired video mode by
sending device commands.
It's a bit confusing that the "current" process is not actually running
while we're inside the scheduler. Perhaps the scheduler should redirect
"current" to its own dummy Process. I'm not sure.
Regardless, this patch improves responsiveness by allowing the scheduler
to unblock a process right after it calls select() in case it already has
a pending wakeup request.
Instead of memcpy'ing the entire screen every time we press enter at the
bottom, use the VGA start address register to make a "view" onto the
underlying memory that moves downward as we scroll.
Eventually we run out of memory and have to reset to the start of the
buffer. That's when we memcpy everything. It would be cool if there was
some way to get the hardware to act like a ring buffer with automatic
wrapping here but I don't know how to do that.
