arm64: mm: Drop dead code for pud special bit handling

Keith Busch observed some incorrect macros defined in arm64 code [1].

It turns out the two lines should never be needed and won't be exposed to
anyone, because aarch64 doesn't select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD,
hence ARCH_SUPPORTS_PUD_PFNMAP is always N.  The only archs that support
THP PUDs so far are x86 and powerpc.

Instead of fixing the lines (with no way to test it..), remove the two
lines that are in reality dead code, to avoid confusing readers.

Fixes tag is attached to reflect where the wrong macros were introduced,
but explicitly not copying stable, because there's no real issue to be
fixed.  So it's only about removing the dead code so far.

[1] https://lore.kernel.org/all/[email protected]/#t

Cc: Alex Williamson <[email protected]>
Cc: Donald Dutile <[email protected]>
Cc: Will Deacon <[email protected]>
Fixes: 3e509c9 ("mm/arm64: support large pfn mappings")
Reported-by: Keith Busch <[email protected]>
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Donald Dutile <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: xzpeter

arch/arm64/include/asm/pgtable.h

@@ -633,11 +633,6 @@ static inline pud_t pud_mkhuge(pud_t pud)
 #define pud_pfn(pud)		((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT)
 #define pfn_pud(pfn,prot)	__pud(__phys_to_pud_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
 
-#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
-#define pud_special(pte)	pte_special(pud_pte(pud))
-#define pud_mkspecial(pte)	pte_pud(pte_mkspecial(pud_pte(pud)))
-#endif
-
 #define pmd_pgprot pmd_pgprot
 static inline pgprot_t pmd_pgprot(pmd_t pmd)
 {