drivers: uio: Kconfig: add MMU dependancy for UIO

The User space I/O drivers are useful, only when user space meaningful
(MMU must be enabled).

So need let it depend on MMU, or can not pass compiling, the related
error (allmodconfig for H8300):

    CC [M]  drivers/uio/uio.o
  drivers/uio/uio.c: In function 'uio_mmap_physical':
  drivers/uio/uio.c:650:2: error: implicit declaration of function 'pgprot_noncached' [-Werror=implicit-function-declaration]
  drivers/uio/uio.c:650:20: error: incompatible types when assigning to type 'pgprot_t' from type 'int'

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>