AMD boards: Fix comment style and typos

Change-Id: Id630cc46b79a39e1786d42adbc21f3b9c3a051aa
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/6118
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>