s390x: lib: Add idte and other huge pages functions/macros

Improve pgtable.h:

* add macros to check whether a pmd or a pud are large / huge
* add idte functions for pmd, pud, p4d and pgd

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20210611140705.553307-5-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>