At the moment, the SMMUv3 unit tests assume ATS is always enabled,
although this is sufficient to test hitless/non-hitless transitions,
but exercising other features is useful to check ste/cd population
logic (for example the .get_used logic).

Add an enum where bits define features per-master, at the moment there
is only ATS and STALLs which are mutually exclusive, but this would
make it easier to extend with other features in the future.

Also, Add 2 more tests for s1 <-> s2 transitions with stalls enabled.
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20240830110349.797399-3-smostafa@google.comSigned-off-by: Will Deacon <will@kernel.org>