samples: drivers: led pwm running on pwm led of the nucleo boards

Configure the overlay file to run the samples/drivers/led_pwm
on the nucleo_l073rz and nucleo_f091rc board.
The green led is used on pa5 for pwm channels of timers2 channel
The leds node has to be disabled to let the pin for the pwm nodes.
The spi1 is disabled in that sample to avoid conflict on pa5 pin.

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