Include rpcsvc into a top-level xHAL

Description

To be merged after !115 (merged).

This MR aims at cleaning up the xHAL and rpcsvc code for future easier maintenance and compilation.

The two major changes are:

1. The promotion of xHAL to a top-level component of cmsgemos.
2. The inclusion of rcpsvc into xHAL, opening the door to a complete absorption and then suppression of the former.

More clean-up to follow, particularly the removal of the Protobuf serialization.

Related Issue

Closes #102 (closed) and #106 (closed) (clean-up of the fix to come later).

How Has This Been Tested?

• The code compiles;
• It is possible to that a run.

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)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.