iommu/arm-smmu-v3: Move context descriptor code

hulk inclusion
category: feature
bugzilla: 14369
CVE: NA
-------------------

In preparation for substream ID support, move the context descriptor code
into a separate module. At the moment it only manages context descriptor
zero, which is used for non-PASID translations.

One important behavior change is the ASID allocator, which is now global
instead of per-SMMU. If we end up needing per-SMMU ASIDs after all, it
would be relatively simple to move back to per-device allocator instead
of a global one. Sharing ASIDs will require an IDR, so implement the
ASID allocator with an IDA instead of porting the bitmap, to ease the
transition.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Fang Lijun <fanglijun3@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>