cxl/region: Translate HPA to DPA and memdev in unaligned regions

cxl/region: Translate HPA to DPA and memdev in unaligned regions

The CXL driver supports an expert user debugfs interface to inject and
clear poison by a region offset. That feature requires translating a
HPA (the region address) to a DPA and a memdev to perform the poison
operation.

Unaligned regions do not have an algebraically invertible mapping
from HPA to DPA due to the region offset skew. The region base is not
aligned to a full interleave. Add a helper to perform the unaligned
translations that first calculates the DPA offset and then tests it
against each candidate endpoint decoder.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/f338b7aff7e4574fcc525b1a0d4f09786bfb6489.1768538962.git.alison.schofield@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>