test: pwm: Add nucleo_h743zi (stm32h7xx) board to loopback test

This commit allows testing the PWM (timers) on the
nucleo_h743zi development board.

The HW setup for testing:
Timer2 (channel 2) as PWM signal generator -> CN11 connector
(PIN 30)

Timer5 (channel1) in Capture mode to measure the pulse
duration -> CN11 connector (PIN28)

Such setup allows easy HW loopback connection (just short cut two
consecutive pins/soldering vias on the devel board's PCB).

Signed-off-by: Lukasz Majewski <lukma@denx.de>