Bluetooth: btrtl: split the device initialization into smaller parts

Bluetooth: btrtl: split the device initialization into smaller parts

This prepares the btrtl code so it can be used to initialize Bluetooth
modules connected via UART (these are found for example on the RTL8723BS
and RTL8723DS SDIO chips, which come with an embedded UART Bluetooth
module).

The Realtek "rtl8723bs_bt" and "rtl8723ds_bt" userspace Bluetooth UART
initialization tools (rtk_hciattach) use the following sequence:
1) send H5 sync pattern (already supported by hci_h5)
2) get LMP version (already supported by btrtl)
3) get ROM version (already supported by btrtl)
4) load the firmware and config for the current chipset (already
   supported by btrtl)
5) read UART settings from the config blob (currently not supported)
6) send UART settings via a vendor command to the device (which changes
   the baudrate of the device and enables or disables flow control
   depending on the config)
7) change the baudrate and flow control settings on the host
8) send the firmware and config blob to the device (already supported by
   btrtl)

The main reason why the initialization has to be split is step #7. This
requires changes to the underlying "bus", which should be kept outside
of the "generic" btrtl driver.
The idea for this split is borrowed from the btbcm driver but adjusted
where needed (the btrtl driver for example needs two blobs: firmware and
config, while the btbcm only needs one).

This also prepares the code for step #5 (parsing the config blob) by
centralizing the code which loads the firmware and config blobs and
storing the result in the new struct btrtl_device_info.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>