Bluetooth: hci_bcm: Retrieve UART speed from ACPI

Parse platform_device's ACPI to retrieve UART init speed.
When BCM device is open, check if its TTY has same parent as one of the
platform devices saved. If yes, use platform_device's init speed.

Signed-off-by: Frederic Danis <frederic.danis@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>