s390/mm: Replace the CSP instruction with CSPG

s390/mm: Replace the CSP instruction with CSPG

The CSPG instruction is part of the Dat-Enhancement facility 1, which
is always available. Given that it can be used everywhere where also
the CSP instruction can be used, replace CSP with CSPG everywhere.

This allows to remove the csp() inline assembly. Also remove the
unused gmap_pmdp_csp() function.

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>