Rework of half bridge driver

[martinjaeger]

The half bridge driver should be reworked to allow having multiple phases in parallel. This might also lead to a more generic complementary PWM signal driver that can be upstreamed to Zephyr.

Name suggestions:

• half_bridge (as it is now)
• sync_pwm
• complementary_pwm (possibly the more correct term, but very long)
• cpwm (short for complementary_pwm)

New features:

• Synchronize multiple channels / phases for multi-phase buck converter

Improved API naming:

• cpwm_get_period_ticks instead of half_bridge_get_arr
• cpwm_get_pulse_ticks instead of half_bridge_get_ccr

[atochukwu0]

You once mentioned that you will not consider multi phase buck, which was a turn off for me at the time , am glad you are introducing this feature .