dts: arm: nuvoton: add PWM nodes for numaker m333x

[cyliangtw]

This PR is to add PWM nodes for Nuvoton NuMaker M333X series.
Also add support of Nuvoton numaker board numaker_m3334ki in pwm_gpio_loopback test.

Test results on numaker_m3334ki board are as follows:

===================================================================
TESTSUITE pwm_gpio_loopback succeeded

------ TESTSUITE SUMMARY START ------

SUITE PASS - 100.00% [pwm_gpio_loopback]: pass = 2, fail = 0, skip = 0, total = 2 duration = 0.885 seconds
 - PASS - [pwm_gpio_loopback.test_pwm] duration = 0.264 seconds
 - PASS - [pwm_gpio_loopback.test_pwm_cross] duration = 0.621 seconds

------ TESTSUITE SUMMARY END ------

===================================================================
PROJECT EXECUTION SUCCESSFUL

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud