Read the vbios directly from the rom.  In some cases,
e.g., virtualization, the rom is not available via
the BAR or other means.  Access it directly.

This is an updated version of Monks original patch which
uses family specific callbacks and unifies some of the
validation checking.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>