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>