unicore32: remove flush_cache_user_range

flush_cache_user_range is an ARMism not used by any generic or unicore32
specific code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Guan Xuetao <gxt@pku.edu.cn>
Link: http://lkml.kernel.org/r/20200515143646.3857579-5-hch@lst.de


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>