Add support for address translation of the PC prior to ifetch

[relokin]

This PR changes the type of Label and makes one of the two types of Symbolic Virtual Constants. This way a Label can be translated and mapped to a Symbolic Physical Constant. Leveraging this, herd7 when self and vmsa are both enabled, for instructions with labels, it introduces a Implicit Read event to Symbolic Virtual Label as well as a branching decision. Much like for data translation for instruction fetches can raise faults.

[relokin]

There are a few things that are work in progress:

• Support in litmus (requires support for self in kvm mode first)
• herd7 should translate all instructions with labels, regardless of whether there is a register initialized to that label or not
• Do we need a new mode vmsa-instr? If yes, we could rename vmsa to vmsa-data make vmsa a variant that enables both. Or otherwise we keep vmsa as is and when we use both vmsa and self we enable this functionality.

[jalglave]

hi @relokin is there any reason to keep this as a draft? How can we help progress on this?
Thanks in advance,
Jade