arch/kunmap: remove duplicate kunmap implementations

All architectures do exactly the same thing for kunmap(); remove all the
duplicate definitions and lift the call to the core.

This also has the benefit of changing kmap_unmap() on a number of
architectures to be an inline call rather than an actual function.

[akpm@linux-foundation.org: fix CONFIG_HIGHMEM=n build on various architectures]
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christian König <christian.koenig@amd.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Helge Deller <deller@gmx.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200507150004.1423069-5-ira.weiny@intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/include/asm/highmem.h

@@ -20,8 +20,6 @@
 
 extern pte_t *pkmap_page_table;
 
-extern void kunmap_high(struct page *page);
-
 /*
  * The reason for kmap_high_get() is to ensure that the currently kmap'd
  * page usage count does not decrease to zero while we're using its
@@ -62,7 +60,6 @@ static inline void *kmap_high_get(struct page *page)
  * when CONFIG_HIGHMEM is not set.
  */
 #ifdef CONFIG_HIGHMEM
-extern void kunmap(struct page *page);
 extern void *kmap_atomic(struct page *page);
 extern void __kunmap_atomic(void *kvaddr);
 extern void *kmap_atomic_pfn(unsigned long pfn);