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'

---
 drivers/uio/Kconfig |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index a81d163..f91ec11 100644
@@ -1,5 +1,6 @@
 menuconfig UIO
 	tristate "Userspace I/O drivers"
+	depends on MMU
 	help
 	  Enable this to allow the userspace driver core code to be
 	  built.  This code allows userspace programs easy access to

1.7.7.6