When booting an SN system without specifing a console
(i.e., no "console=" on boot line), the system will hang during
boot at the point where /sbin/init is run.

The problem is that vga_console_iobase is not converted to a
virtual address before storing in io_space[0].mmio_base.
The conversion was happening in sn_scan_pcdp(), but not in
setup_vga_console().
Signed-off-by: John Keller <jpk@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>