ARM: 9305/1: add clear/copy_user_highpage declarations

The CPU specific helpers have to be global functions when building
a kernel for just one CPU, but are called through indirect function
pointers in a multi-CPU kernel. This config currently lacks the
declarations for the individual helpers, e.g.:

arch/arm/mm/copypage-v4wb.c:47:6: error: no previous prototype for 'v4wb_copy_user_highpage' [-Werror=missing-prototypes]
arch/arm/mm/copypage-v4wb.c:65:6: error: no previous prototype for 'v4wb_clear_user_highpage' [-Werror=missing-prototypes]

Add the complete set of prototypes in asm/page.h to allow
building iwth -Wmissing-prototypes.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>