Allow to tune installation directories

The location of intrinsic bindings and samples could not be tuned
but was fixed to be ${CMAKE_INSTALL_FULL_LIBDIR}/afb and
${CMAKE_INSTALL_FULL_DATADIR}/af-binder

These default locations are not bad but it is important to be able
to tune that location.

Bug-AGL: SPEC-2367

Change-Id: I4d4f9e9490d61e3278ef35ac42f2143a752a7c37
Signed-off-by: José Bollo <jose.bollo@iot.bzh>