AMD/IOMMU: allow callers to request allocate_buffer() to skip its memset()

AMD/IOMMU: allow callers to request allocate_buffer() to skip its memset()

The command ring buffer doesn't need clearing up front in any event.
Subsequently we'll also want to avoid clearing the device tables.

While playing with functions signatures replace undue use of fixed width
types at the same time, and extend this to deallocate_buffer() as well.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>