riscv64/pmap: fix not currently mapped memory being accessed

[lukileczo]

Description

When executing (v)fork, first the memory map is copied and then the new process switches to that map. On risc-v, when mapping new page, cache is invalidated. However, the invalidation may cause page fault when the virtual address is not mapped in the context of currently used memory map. This PR fixes this by switching to the memory map in which the address is mapped, executing the flush/inval and returning to original memory map.

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: riscv64-noelv-fpga

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.