[surfman] Assume the hack.

Export xen_get_framebuffer() interface in hw/xen.h.
Sort out headers in ui/surfman.c.
Refresh patches
[vgabios] Add spinlock on ioport 0x3800.

Mechanism implemented in XT as some concurency was suspected in int10h
calls (test case yet to be found).
Adds a 2 bytes ioport region in qemu @0x3800 to behave like a spinlock.
See use in vgabios corresponding patch.
[vgabios] Add 0x3802 IO port to shadow BDA data.

vgabios uses BDA to stash information that will later be used in BIOS
call (int10h), but BDA tends to be thrashed once the BIOS is done and
various sources tend to say it is not required to be preserved that long
anyway.

So add ioports 0x3800->0x383F to those informations.
See use in vgabios patch.
[surfman] Fix the patch

Fix the quilt screw up.
Fix indentation mess.
Improve the debug a bit, use a global variable for SurfmanState so we
can have another DCL running for comparison.