mainboard/amd: De-ASCIIartify AGESA board headers

As was done for the reference boards in:

cd30951 mainboard/amd: De-ASCIIartify reference boards

Change-Id: Ie34aa5269388b771daa6934f8aff0314ac6778d5
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6290
Tested-by: build bot (Jenkins)
Reviewed-by: Dave Frodin <dave.frodin@se-eng.com>