Small changes into the Ariane

Created by: lvcargnini

I spread some modules from the frontend into multiple files, just for the organization of the design, instead of a single file containing multiple modules I place each module in its file.

Also, I added four modules, one it is a generic that IC flows and FPGA flows translate into an asynchronous DFF. Also added a register model based on it. Added two generic SRAM modules, that on FPGA will be translated into its counterpart on BRAM automatically. Needs to be improved to support both IC and FPGA flows, for it works on FPGA, on ASIC it creates a sea of DFFs.