xtensa: implement clear_user_highpage and copy_user_highpage

Existing clear_user_page and copy_user_page cannot be used with highmem
because they calculate physical page address from its virtual address
and do it incorrectly in case of high memory page mapped with
kmap_atomic. Also kmap is not needed, as most likely userspace mapping
color would be different from the kmapped color.

Provide clear_user_highpage and copy_user_highpage functions that
determine if temporary mapping is needed for the pages. Move most of the
logic of the former clear_user_page and copy_user_page to
xtensa/mm/cache.c only leaving temporary mapping setup, invalidation and
clearing/copying in the xtensa/mm/misc.S. Rename these functions to
clear_page_alias and copy_page_alias.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/cacheflush.h

@@ -37,6 +37,7 @@
  * specials for cache aliasing:
  *
  * __flush_invalidate_dcache_page_alias(vaddr,paddr)
+ * __invalidate_dcache_page_alias(vaddr,paddr)
  * __invalidate_icache_page_alias(vaddr,paddr)
  */
 
@@ -62,6 +63,7 @@ extern void __flush_invalidate_dcache_range(unsigned long, unsigned long);
 
 #if defined(CONFIG_MMU) && (DCACHE_WAY_SIZE > PAGE_SIZE)
 extern void __flush_invalidate_dcache_page_alias(unsigned long, unsigned long);
+extern void __invalidate_dcache_page_alias(unsigned long, unsigned long);
 #else
 static inline void __flush_invalidate_dcache_page_alias(unsigned long virt,
 							unsigned long phys) { }