uart_ns16550 broken on ITE, Realtek and possibly more

[fabiobaltieri]

Describe the bug

uart_ns16550 is broken on ITE, Realtek and possibly more platforms since fd88386.

More details on #93568 but the tl;dr is that the feature should have probably been implementation specific and does not play well with system managed PM.

Regression

• This is a regression.

Steps to reproduce

Flash the shell sample on an ITE board, uart is unresponsive.

Relevant log output

Impact

Showstopper – Prevents release or major functionality; system unusable.

Environment

Linux, Zephyr SDK, fd88386

Additional Context

No response

[fabiobaltieri]

Let's call it medium since I haven't actually verified it breaks other platforms but even if it doesn't it certainly does not help any.

[fabiobaltieri]

Verified the regression is reproducible on rts5912 as well

[fabiobaltieri]

High since it impacts multiple platforms.