lenovo/t520: update Kconfig

override default ivy VGA_BIOS_ID
add model & part number
Remove ARCH_X86 as is in,
  fd33781 Move ARCH_* from board/Kconfig to cpu or soc Kconfig.

Change-Id: I61dc6434de7af2d8672f784df87a8b9d3f0fb068
Signed-off-by: Nicolas Reinecke <nr@das-labor.org>
Reviewed-on: http://review.coreboot.org/6759
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>