[FEATURE] Re-usable 16550 UART driver

### Is your feature request related to a problem? Please describe.

the same issue like for PL011: https://github.com/apache/nuttx/issues/18836

### Describe the solution you'd like

Modify the 16550 UART driver so that individual boards can use the C API to:

Register as many UARTs as they need
Control interrupt registration
Define their own Kconfig options for selecting active UART interfaces/options

Part of the code is already adapted to these changes due to support for PCI cards

### Describe alternatives you've considered

_No response_

### Verification

- [x] I have verified before submitting the report.