xen: allow enable use of VGA console on dom0

xen: allow enable use of VGA console on dom0

Get the information about the VGA console hardware from Xen, and put
it into the form the bootloader normally generates, so that the rest
of the kernel can deal with VGA as usual.

[ Impact: make VGA console work in dom0 ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
[v1: Rebased on 2.6.39]
[v2: Removed incorrect comments and fixed compile warnings]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
(cherry picked from commit c2419b4a4727f67af2fc2cd68b0d878b75e781bb)

Conflicts:
	arch/x86/xen/Makefile
	arch/x86/xen/enlighten.c
	arch/x86/xen/xen-ops.h