Bluetooth: Controller: Replace BT_CTLR with HAS_BT_CTLR

Deprecate BT_CTLR, and add a new HAS_BT_CTLR as a virtual option which
specific users (like BT_LL_SW_SPLIT) select. This also means that we can
remove all places that were forcefully enabling the BT_CTLR option, and
instead we now depend on devicetree to get some local LL HCI driver
enabled which in turn also enables the HAS_BT_CTLR option.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>