google/auron: Add mainboard

Add the Google Auron Broadwell Reference Mainboard. It is based
on the Google Peppy mainboard. It was merged from the following
chromium.org commit:  d20a1d1a22d64546a5d8761b18ab29732ec0b848

Change-Id: I716a79e198e91c428bd965fcd03665c2c7067602
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/10500
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
36 files changed