cxl/mem: Force array size of mem_commands[] to CXL_MEM_COMMAND_ID_MAX

cxl/mem: Force array size of mem_commands[] to CXL_MEM_COMMAND_ID_MAX

Typically the mem_commands[] array is in sync with 'enum { CXL_CMDS }'.
Current code works well.

However, the array size of mem_commands[] may not strictly be the same
as CXL_MEM_COMMAND_ID_MAX. E.g. if a new CXL_CMD() is added that is
guarded by #ifdefs, the array could be shorter. This could lead then
further to an out-of-bounds array access in cxl_validate_cmd_from_user().

Fix this by forcing the array size to CXL_MEM_COMMAND_ID_MAX. This
also adds range checks for array items in mem_commands[] at compile
time.

Signed-off-by: Robert Richter <rrichter@amd.com>
Link: https://lore.kernel.org/r/20210324141635.22335-1-rrichter@amd.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>