morello: Add support for QEMU platform

[heshamelmatary]

This was tested on a baseline AArch64 Morello/QEMU without CHERI.

Basic support for a PL011 driver.

[axel-h]

Do you expect this to match the hardware, so we'd put this in a morello folder and not morello-qemu

[axel-h]

Since this created another PL011 driver, it could be put on top of https://github.com/seL4/util_libs/pull/157 to reduce the duplication a bit.

[heshamelmatary]

Do you expect this to match the hardware, so we'd put this in a morello folder and not morello-qemu

Not quite. PL011's address and IRQ are different. Also hardware has extra clock, pl011, and timer (SP804) drivers. Unfortunately, I don't think drivers can be currently shared in util_libs.

[heshamelmatary]

Since this created another PL011 driver, it could be put on top of #157 to reduce the duplication a bit.

I believe that's the right direction, but are there plans to merge #157 soon? If not, we could just merge this and then remove later not to block https://github.com/seL4/seL4/issues/1158 ?