Bluetooth: hci_bcm: Support platform enumeration

Until now the driver supports only ACPI enumeration. Nevertheless
Intel Edison SoM has Broadcom Wi-Fi + BT chip and neither ACPI nor DT
enumeration mechanism.

Enable pure platform driver in order to support Intel Edison SoM.

Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>