x86, uv: Add serial number parameter to uv_bios_get_sn_info()

Add system_serial_number to the information returned by
uv_bios_get_sn_info() UV BIOS call.

Signed-off-by: Russ Anderson <rja@sgi.com>
LKML-Reference: <20091217165323.GA30774@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>