asm-generic: add a flush_icache_user_range stub

Define flush_icache_user_range to flush_icache_range unless the
architecture provides its own implementation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/20200515143646.3857579-21-hch@lst.deSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/cacheflush.h

@@ -66,6 +66,10 @@ static inline void flush_icache_range(unsigned long start, unsigned long end)
 }
 #endif
 
+#ifndef flush_icache_user_range
+#define flush_icache_user_range flush_icache_range
+#endif
+
 #ifndef flush_icache_page
 static inline void flush_icache_page(struct vm_area_struct *vma,
 				     struct page *page)