Makefiles

Hi Aimme. This pull-request implements the change to the Makefiles for uvmt_cv32 that I mentioned to you in MatterMost:

cv32/sim/
      +--- Common.mk
      +--- uvmt_cv32/
                     +--- Makefile
                     +--- vsim.mk
                     +--- dsim.mk
                     +--- xrun.mk
                     +--- <other_simulators>.mk

I have tested it with dsim and xrun, but lack the ability to test it with vsim.