southbridge/amd: Change #if defined to #if IS_ENABLED

The IMC functions were being called and timing out when the
CONFIG_SB800_IMC_FWM/CONFIG_HUDSON_IMC_FWM were defined as 0.
Changing to a IS_ENABLED will keep the IMC handshake from
occuring if the IMC firmware isn't running.

Tested on a Persimmon platform which makes three calls to
spi_claim_bus() with each call timing out after 500ms.

Change-Id: I5d4bbcecf003b93704553b495a16bcd15f66763b
Signed-off-by: Dave Frodin <dave.frodin@se-eng.com>
Reviewed-on: http://review.coreboot.org/5974
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
2 files changed