Bluetooth: hci_mrvl: Add serdev support for 88W8997

Add serdev support for the 88W8997 from NXP (previously Marvell). It
includes support for changing the baud rate. The command to change the
baud rate is taken from the user manual UM11483 Rev. 9 in section 7
(Bring-up of Bluetooth interfaces) from NXP.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>