Bluetooth: hci_h5: btrtl: Add support for RTL8821CS

RTL8821CS is a WiFi + Bluetooth combo chip from Realtek that provides
WiFi A/B/G/N/AC over an SDIO interface and Bluetooth 4.2 over a UART
interface.

Note that the firmware this was tested with was firmware version
0x75b8f098.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>