acpi: add support for the XSDT

[dlrobertson]

Summary

We currently only support the 32-bit RSDT, but should also support the 64-bit XSDT.

Details

We do not return the RSDT if the RSDP version corresponds to ACPI 2.0.

https://github.com/mythril-hypervisor/mythril/blob/master/mythril_core/src/acpi/rsdp.rs#L203

There are several locations where we assume the pointer size to be 32 bits

https://github.com/mythril-hypervisor/mythril/blob/master/mythril_core/src/acpi/rsdt.rs#L167

[ntegan]

yes

[ntegan]

Got it working but need to clean up

https://github.com/ntegan/mythril/tree/54-xsdt