feature(target): define VADDR_KERNEL

[badochov]

JIRA: RTOS-908

Description

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: (list targets here).

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
  feature(pmap): define VADDR_KERN in makefile phoenix-rtos-kernel#585
  feature(hal): rename VADDR_KERNEL_INIT to VADDR_KERNEL plo#343
• I will merge this PR by myself when appropriate.

[badochov]

Project PR showing it works: phoenix-rtos/phoenix-rtos-project#1159