Bluetooth: hci_bcm: Enable parsing of LM_DIAG messages

The Broadcom UART based controllers can send LM_DIAG messages with the
identifier 0x07 inside the HCI stream. These messages are 63 octets in
size and have no variable payload or length indicator.

This patch adds correct parsing information for the h4_recv_buf handler
and in case these packets are received, they are forwarded to the
Bluetooth core via hci_recv_diag interface.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>