CRIS: Export missing function symbols

strcmp was lost when all other string functions were removed,
but we still have an optimized version for this on CRISv32,
so any driver built as a module would not have access to this symbol.

In a similar manner, we had optimized versions of
csum_partial_copy_from_user and __do_clear_user
but no exported symbols for them, breaking bunch of other drivers
when built as a module.

At the same time, move EXPORT_SYMBOL(__copy_user) and
EXPORT_SYMBOL(__copy_user_zeroing) C-files so it's
located together with the function definition.

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>