powerpc/4xx: Add 16K FIFO size DTS entries on supported platforms

Adding tx/rx-fifo-size-gige to EMAC fields for evaluation kit DTS
files where appropriate.

Signed-off-by: Dave Mitchell <dmitchell@appliedmicro.com>
Acked-by: Prodyut Hazarika <phazarika@appliedmicro.com>
Acked-by: Victor Gallardo <vgallardo@appliedmicro.com>
Acked-by: Loc Ho <lho@appliedmicro.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>