lib: s390x: add header for CMM related defines

Since we're going to need the definitions in an upcoming migration test for CMM,
add a header for CMM related defines. It is based on
arch/s390/include/asm/page-states.h from linux.

While at it, use the constants in existing calls to CMM related functions.

Also move essa() and test_availability() there to be able to use it outside
cmm.c.

Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>