vmm: refactor event reflection in AMD SVM

[bnovkov]

Summary

This patch refactors AMD SVM event reflection to allow events to be propagated to userland, rather than always reflected into the guest.
This is necessary to implement some capabilities that request VMEXITs when a specific exception occurs (e.g. VM_CAP_BPT_EXIT).

This work was sponsored by the GSoC '22 program.

[jhb]

If you merge this first, then the breakpoint patch doesn't need 'handled = 0', right?

[bnovkov]

In D42405#976891, @jhb wrote:

If you merge this first, then the breakpoint patch doesn't need 'handled = 0', right?

Yes, that line is redundant and I've removed it.