Add subsystemid option to sconfig

Add subsystemid option to sconfig

Allow user to add 'subsystemid <vendor> <device> [inherit]' to devicetree.cb for
PCI and PCI domain devices.

Example:

	device pci 00.0 on
	       subsystemid dead beef
	end

If the user wants to have this ID inherited to all subdevices/functions,
he can add 'inherit', like in the following example:

	device pci 00.0 on
	       subsystemid dead beef inherit
	end

If the user don't want to inherit a Subsystem for a single device, he can
specify 'subsystemid 0 0' on this particular device.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6420 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1