cxl/memdev: Change cxl_mem to a more descriptive name

The 'struct cxl_mem' object actually represents the state of a CXL
device within the driver. Comments indicating that 'struct cxl_mem' is a
device itself are incorrect. It is data layered on top of a CXL Memory
Expander class device. Rename it 'struct cxl_dev_state'. The 'struct'
cxl_memdev' structure represents a Linux CXL memory device object, and
it uses services and information provided by 'struct cxl_dev_state'.

Update the structure name, function names, and the kdocs to reflect the
real uses of this structure.

Some helper functions that were previously prefixed "cxl_mem_" are
renamed to just "cxl_".

Acked-by: Ben Widawsky <[email protected]>
Signed-off-by: Ira Weiny <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dan Williams <[email protected]>

Author: weiny2