Kconfig: Move BT_WAIT_NOP into subsys/bluetooth/host

The CONFIG_BT_WAIT_NOP define is used only by
zephyr/subsys/bluetooth/host/hci_core.c.

It is also the only config in drivers/bluetooth that is in use when
BT_CONTROLLER is enabled. Moving it into the bluetooth subsystem
allows us to restructure the drivers/kconfig code such that the entire
Bluetooth driver menu option is omitted when the BT_CONTROLLER is
enabled.

Moving it will also mean that all configs in drivers/bluetooth will
now be related to configuring the source code in drivers/bluetooth.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>