Bluetooth: hci_uart: Add Marvell support

This patch introduces support for Marvell Bluetooth controller over
UART (8897 for now). In order to send the final firmware at full speed,
a helper firmware is firstly sent. Firmware download is driven by the
controller which sends request firmware packets (including expected
size).

This driver is a global rework of the one proposed by
Amitkumar Karwar <akarwar@marvell.com>.

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>