Bluetooth: hci_bcm: Fall back to getting bdaddr from EFI if not set

On some devices the BCM Bluetooth adapter does not have a valid bdaddr set.

btbcm.c currently sets HCI_QUIRK_INVALID_BDADDR to indicate when this is
the case. But this requires users to manual setup a btaddr, by doing e.g.:

btmgmt -i hci0 public-addr 'B0:F1:EC:82:1D:B3'

Which means that Bluetooth will not work out of the box on such devices.
To avoid this (where possible) hci_bcm sets: HCI_QUIRK_USE_BDADDR_PROPERTY
which tries to get the bdaddr from devicetree.

But this only works on devicetree platforms. On UEFI based platforms
there is a special Broadcom UEFI variable which when present contains
the devices bdaddr, just like how there is another UEFI variable which
contains wifi nvram contents including the wifi MAC address.

Add support for getting the bdaddr from this Broadcom UEFI variable,
so that Bluetooth will work OOTB for users on devices where this
UEFI variable is present.

This fixes Bluetooth not working on for example Asus T100HA 2-in-1s.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>