ARM: 9314/1: tcm: move tcm_init() prototype to asm/tcm.h

The function definition is in a file that does not include the
header with the declaration:

arch/arm/kernel/tcm.c:256:13: error: no previous prototype for 'tcm_init'

Move the declaration to a global header where it can actually be
included.

Fixes: de40614e ("ARM: 7694/1: ARM, TCM: initialize TCM in paging_init(), instead of setup_arch()")
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
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>