VPI Targets

Reviewer: @rlane 

Include VPI target build configurations:

targets/vpi/libvpi -- Builds a shared library and debian package for all VPI-based tools. 
targets/vpi/pyvpi -- Builds the python bindings and interface classes for the VPI. (Depends on libvpi). 
targets/vpi/jvpi -- Builds the java native interface classes for VPI. (Depends on libvpi)
targets/vpi/vpitool -- Moved from targets/vpitool