Use RVec instead of float for x, v and f device buffers

Use RVec instead of float for x, v and f device buffers

Using RVec instead of float for coordinates data-types allows to
remove multiplications by DIM when the adresses, offsets and sizes
are computed. Since the native device types are not used in CPU
part of the code, the type casting remains.

Refs #3312 and #2936

Change-Id: Iaea914a474195f214ca860f7345f6878b9a04813