packagegroup-webos-extended: Use VIRTUAL-RUNTIME for rdx components

Add VIRTUAL-RUNTIME_librdx and VIRTUAL-RUNTIME_rdx-utils and set their
defaults to the stub components.

Open-webOS-DCO-1.0-Signed-off-by: Gayathri Srinivasan <gayathri.srinivasan@lge.com>
Change-Id: I94e8b006000dafab1626b3fa01dfb37d0879afc3
Reviewed-on: https://g2g.palm.com/1673
Tested-by: Gayathri Srinivasan <gayathri.srinivasan@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>