mips: drop definition of pfn_valid() for DISCONTIGMEM

There is a stale definition of pfn_valid() for DISCONTINGMEM memory model
guarded !FLATMEM && !SPARSEMEM && NUMA ifdefery.

Remove everything but definition of pfn_valid() for FLATMEM.

Link: https://lkml.kernel.org/r/20230129124235.209895-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Brian Cain <bcain@quicinc.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Huacai Chen <chenhuacai@loongson.cn>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Rich Felker <dalias@libc.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/mips/include/asm/page.h

@@ -235,21 +235,6 @@ static inline int pfn_valid(unsigned long pfn)
 	return pfn >= pfn_offset && pfn < max_mapnr;
 }
 
-#elif defined(CONFIG_SPARSEMEM)
-
-/* pfn_valid is defined in linux/mmzone.h */
-
-#elif defined(CONFIG_NUMA)
-
-#define pfn_valid(pfn)							\
-({									\
-	unsigned long __pfn = (pfn);					\
-	int __n = pfn_to_nid(__pfn);					\
-	((__n >= 0) ? (__pfn < NODE_DATA(__n)->node_start_pfn +		\
-			       NODE_DATA(__n)->node_spanned_pages)	\
-		    : 0);						\
-})
-
 #endif
 
 #define virt_to_pfn(kaddr)   	PFN_DOWN(virt_to_phys((void *)(kaddr)))