tests: drivers: uart async on nucleo_wb55rg with DMA

Configure through an overlay file, the nucleo_wb55rg board
for running the tests/drivers/uart/uart_async_api.
DMAMUX is used for transfer on channels 0 & 1 with
LPUART peripheral request 17 & 16.
No hw flowcontrol for this test.
Connect pin A0 & A1 of CN8 to PASS the test.
Note that I2C3 pin assignment might conflict (PC0 & PC1).

Signed-off-by: Francois Ramu <francois.ramu@st.com>