drivers: bluetooth: hci: Introduce ST SPI protocol V2

Introduce STMicroelectronics SPI protocol V2 which is used in BlueNRG-1
and successor devices.

Change the size of the variable "size" to 16 bits as it is necessary for ST
BlueNRG-1 and successor devices.

Signed-off-by: Ali Hozhabri <ali.hozhabri@st.com>