vendorcode/amd/agesa/f15tn: Fix GnbIommuScratch in AGESA compilation

Missing IOMMU support is missing from the libagesa Makefile, it also
lacks a header with type-signature and a few bad typecast issues.

Change-Id: I7f2ad2104de9baaa66dbb6ffeb0f2b4d35fa5c16
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Co-Author: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/7642
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
3 files changed