sh: Kill off __{copy,clear}_user_page().

Now that copy_to_user_page()/copy_from_user_page() are wired up, we
can drop the old __copy_xxx() implementations. Now that the page
colouring scheme has changed via kmap_coherent(), we can avoid the
flush in these specific helpers.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>