drivers: bluetooth: hci: Multiple write transaction support for BlueNRG-MS

Provide multiple write transaction support for BlueNRG-MS, st_hci_spi_v1
protocol. Since by default, BlueNRG-MS write buffer supports up to 127
bytes; however, it is possible to have consecutive write transactions
so as to send data more than 127 bytes.

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