[ARM] 4502/1: nommu: Do not export the copy/clear user page functions

The __cpu_{clear|copy}_user_page functions are not defined for the
MMU-less case and therefore should not be exported.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>