The code to mark a page as icache dirty (so that it will later be
icache-dcache flushed when we try to execute from it) is duplicated in
three places: flush_dcache_page() does this marking and nothing else,
but clear_user_page() and copy_user_page() duplicate it, since those
functions make the page icache dirty themselves.
This patch makes those other functions call flush_dcache_page()
instead, so the logic's all in one place. This will make life less
confusing if we ever need to tweak the details of the the lazy icache
flush mechanism.