drivers: staging: android: Kconfig: add depends on MMU for ANDROID_BINDER_IPC

ANDROID_BINDER_IPC used the functions which need depend on MMU, so need
let it depend on MMU too, or compiling fails.

The related error:

  drivers/built-in.o: In function `binder_update_page_range':
  drivers/staging/android/binder.c:599: undefined reference to `map_vm_area'
  drivers/staging/android/binder.c:626: undefined reference to `zap_page_range'
  drivers/built-in.o: In function `binder_mmap':
  drivers/staging/android/binder.c:2744: undefined reference to `get_vm_area'

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