serial: 8250_mid: fix broken DMA dependency

In order to enable HSU DMA PCI driver, the HSU DMA Engine
must be enabled. This add a check for that.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>