config: Set CONFIG_SERIAL_DEV_CTRL_TTYPORT=y in Raspberry Pi defconfigs

The next patch adds a device tree overlay for Bluetooth. The Bluetooth
device node is a child of uart0 (pl011). The children of pl011 are not
registered as platform devices by of_platform_bus_create, because they
fall into `of_device_is_compatible(bus, "arm,primecell")` check. These
children are registered by of_serdev_register_devices, called through
this chain of calls:

  - uart_add_one_port (drivers/tty/serial/amba-pl011.c)
  - tty_port_register_device_attr_serdev
  - serdev_tty_port_register
  - serdev_controller_add
  - of_serdev_register_devices

serdev_tty_port_register depends on CONFIG_SERIAL_DEV_CTRL_TTYPORT,
which in turn depends on CONFIG_SERIAL_DEV_BUS=y. This patch modifies
the defconfigs of Raspberry Pi devices to set these options and allow
to bind drivers to subnodes of UART devices that can be added by device
tree overlays.

Signed-off-by: Maxim Mikityanskiy <maxtram95@gmail.com>