tests: drivers: pwm driver running on the stm32h573 disco kit

Add the overlay to run the pwm_loopback testcase on the
stm32h573i_dk platform.
Connect D3 (pin 4 of CN15) to D10 (pin 3 of CN13) to pass the test

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