drivers: serial: NXP uart_mcux_flexcomm: instance interrupt config not saved during PM_DEVICE_ACTION_TURN_OFF

[DerekSnell]

Describe the bug

The PM action saves the interrupts enabled using a global variable called usart_intenset. The problem is when you have multiple uart instances that have different configurations, when entering/exiting from a power level, only one configuration is saved and will be applied to all uart instances when exiting from a power level. We need to keep this setting individual for each instance.

Regression

• This is a regression.

Steps to reproduce

1. Enable multiple UART instances
2. Select CONFIG_PM=y and enabled the standby node for PM3 mode
3. Force the app to enter the Idle state for at least 351ms so the PM policy will enter Standby (PM3) mode

The INTEN register for all UART instances will be saved and then restored using the single usart_intenset variable.

Relevant log output

Impact

Functional Limitation – Some features not working as expected, but system usable.

Environment

No response

Additional Context

No response

[DerekSnell]

Fixed by #100187