[FEATURE] RPi 4B PL011 UART support

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

Currently, the only supported UART interface for the Pi 4B is the auxiliary Mini-UART interface, which is used as the shell.

### Describe the solution you'd like

Support for all of the PL011 UARTs should be added. PL011 is a standard UART implementation and it is supported already by some of the virtual targets. I would like the driver to be converted to an upper-half implementation so that each architecture can implement its own lower-half (i.e. just provide a register bank address and interrupt configurations). This way the code can be used for many other PL011 systems in the future.

### Describe alternatives you've considered

Just copying the PL011 implementation and modifying it for the 4B. I don't like this option, it will duplicate code.

### Verification

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