[FEATURE] RPi 4B PL011 UART support

[linguini1]

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

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