Bluetooth: hci_intel: Add Intel baudrate configuration support
Implement the set_baudrate callback for hci_intel.
- Controller requires a read Intel version command before updating
its baudrate.
- The operation consists in an async cmd since the controller does
not respond at the same speed.
- Wait 100ms to let the controller change its baudrate.
- Clear RTS until we change our own UART speed
Manage speed change in the setup function, we need to restore the oper
speed once chip has booted on patched firmware.