arm64/mm: Replace open encodings with PXD_TABLE_BIT

[pgd|p4d]_bad() helpers have open encodings for their respective table bits
which can be replaced with corresponding macros. This makes things clearer,
thus improving their readability as well.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Link: https://lore.kernel.org/r/20250107015529.798319-1-anshuman.khandual@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: Anshuman Khandual

arch/arm64/include/asm/pgtable.h

@@ -896,7 +896,7 @@ static inline bool mm_pud_folded(const struct mm_struct *mm)
 	pr_err("%s:%d: bad pud %016llx.\n", __FILE__, __LINE__, pud_val(e))
 
 #define p4d_none(p4d)		(pgtable_l4_enabled() && !p4d_val(p4d))
-#define p4d_bad(p4d)		(pgtable_l4_enabled() && !(p4d_val(p4d) & 2))
+#define p4d_bad(p4d)		(pgtable_l4_enabled() && !(p4d_val(p4d) & P4D_TABLE_BIT))
 #define p4d_present(p4d)	(!p4d_none(p4d))
 
 static inline void set_p4d(p4d_t *p4dp, p4d_t p4d)
@@ -1023,7 +1023,7 @@ static inline bool mm_p4d_folded(const struct mm_struct *mm)
 	pr_err("%s:%d: bad p4d %016llx.\n", __FILE__, __LINE__, p4d_val(e))
 
 #define pgd_none(pgd)		(pgtable_l5_enabled() && !pgd_val(pgd))
-#define pgd_bad(pgd)		(pgtable_l5_enabled() && !(pgd_val(pgd) & 2))
+#define pgd_bad(pgd)		(pgtable_l5_enabled() && !(pgd_val(pgd) & PGD_TABLE_BIT))
 #define pgd_present(pgd)	(!pgd_none(pgd))
 
 static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)