Lenovo X60/T60: add first_battery setting

Lenovo X60/T60: add first_battery setting

The EC allows to select the order in which batteries are (dis)charged.
Make this setting available to the user.

Change-Id: Id2a98192565419dbb53f3a7cf0b2c46b672a3ed8
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Reviewed-on: http://review.coreboot.org/475
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Peter Stuge <peter@stuge.se>