Verific build support improvements

Support building Yosys with "vanilla" Verific builds

Added/renamed compile parameters
It is possible to compile with various combinations of available supported Verific libraries now
Fixed multiple source file for VHDL
Refactored import/cleanup code to prevent code duplication

Compile parameters:

ENABLE_VERIFIC - enable compiling with Verific library
ENABLE_VERIFIC_SYSTEMVERILOG - Verilog / SystemVerilog support (requires "verilog" dir in Verific lib)
ENABLE_VERIFIC_VHDL - VHDL support (requires "vhdl" dir in Verific lib)
ENABLE_VERIFIC_HIER_TREE - hierarchy tree package support (requires "hier_tree" dir in Verific lib)
ENABLE_VERIFIC_EDIF - EDIF files support (requires "edif" dir in Verific lib)
ENABLE_VERIFIC_LIBERTY - Liberty files support (requires "synlib" dir in Verific lib)
ENABLE_VERIFIC_YOSYSHQ_EXTENSIONS - YosysHQ extensions, only works if you have commercial patch from us

YosysHQ / yosys