cxl/region: Add support to indicate region has extended linear cache

cxl/region: Add support to indicate region has extended linear cache

Add a region sysfs attribute to show the size of the extended linear
cache if there is any. The attribute is invisible when the cache
size is 0, which indicates it does not exist.

Moved the cxl_region_visible() location in order to pick up the
new sysfs attribute definition.

[ dj: Fixed spelling errors noted by Benjamin ]

Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251022203052.4078527-1-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>