cxl/region: Factor out interleave granularity setup

cxl/region: Factor out interleave granularity setup

Region creation based on Type3 devices can be triggered from user space
allowing memory combination through interleaving.

In preparation for kernel driven region creation, that is Type2 drivers
triggering region creation backed with its advertised CXL memory, factor
out a common helper from the user-sysfs region setup for interleave
granularity.

Signed-off-by: Alejandro Lucero <alucerop@amd.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20260228173603.1125109-4-alejandro.lucero-palau@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>