xtensa: remove redundant flush_dcache_page and ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros

xtensa's flush_dcache_page() can be a no-op sometimes. There is a
generic implementation for this case in include/asm-generic/
cacheflush.h.
 #ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
 static inline void flush_dcache_page(struct page *page)
 {
 }

 #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
 #endif

So remove the superfluous flush_dcache_page() definition, which also
helps silence potential build warnings complaining the page variable
passed to flush_dcache_page() is not used.

   In file included from crypto/scompress.c:12:
   include/crypto/scatterwalk.h: In function 'scatterwalk_pagedone':
   include/crypto/scatterwalk.h:76:30: warning: variable 'page' set but not used [-Wunused-but-set-variable]
      76 |                 struct page *page;
         |                              ^~~~
   crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
>> crypto/scompress.c:174:38: warning: unused variable 'dst_page' [-Wunused-variable]
     174 |                         struct page *dst_page = sg_page(req->dst);
         |

The issue was originally reported on LoongArch by kernel test
robot (Huacai fixed it on LoongArch), then reported by Guenter
and me on xtensa.

This patch also removes lots of redundant macros which have
been defined by asm-generic/cacheflush.h.

Cc: Huacai Chen <chenhuacai@loongson.cn>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202403091614.NeUw5zcv-lkp@intel.com/


Reported-by: Barry Song <v-songbaohua@oppo.com>
Closes: https://lore.kernel.org/all/CAGsJ_4yDk1+axbte7FKQEwD7X2oxUCFrEc9M5YOS1BobfDFXPA@mail.gmail.com/


Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/all/aaa8b7d7-5abe-47bf-93f6-407942436472@roeck-us.net/


Fixes: 77292bb8 ("crypto: scomp - remove memcpy if sg_nents is 1 and pages are lowmem")
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Message-Id: <20240319010920.125192-1-21cnbao@gmail.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>