s390/mm: add set_pte_bit()/clear_pte_bit() helper functions

Add set_pte_bit()/clear_pte_bit() and set_pXd_bit()/clear_pXd_bit
helper functions which are supposed to be used if bits within
ptes/pXds are set/cleared.
The only point of these helper functions is to get more readable
code. This is quite similar to what arm64 has.
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -538,6 +538,36 @@ static inline int mm_alloc_pgste(struct mm_struct *mm)
 	return 0;
 }
 
+static inline pte_t clear_pte_bit(pte_t pte, pgprot_t prot)
+{
+	return __pte(pte_val(pte) & ~pgprot_val(prot));
+}
+
+static inline pte_t set_pte_bit(pte_t pte, pgprot_t prot)
+{
+	return __pte(pte_val(pte) | pgprot_val(prot));
+}
+
+static inline pmd_t clear_pmd_bit(pmd_t pmd, pgprot_t prot)
+{
+	return __pmd(pmd_val(pmd) & ~pgprot_val(prot));
+}
+
+static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
+{
+	return __pmd(pmd_val(pmd) | pgprot_val(prot));
+}
+
+static inline pud_t clear_pud_bit(pud_t pud, pgprot_t prot)
+{
+	return __pud(pud_val(pud) & ~pgprot_val(prot));
+}
+
+static inline pud_t set_pud_bit(pud_t pud, pgprot_t prot)
+{
+	return __pud(pud_val(pud) | pgprot_val(prot));
+}
+
 /*
  * In the case that a guest uses storage keys
  * faults should no longer be backed by zero pages