libpayload: rename i386 to x86

Change-Id: Ia9170bd3d04e76dbf9321ca7ea4be23b5e468d21
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/2033
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
20 files changed