cpu/amd/agesa/family1*: Use IS_ENABLED() macro

Change-Id: I54d6871597121392625293027a794d52cf28dd4c
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/7542
Reviewed-by: Bruce Griffith <Bruce.Griffith@se-eng.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>