Add a peripheral 'multi3x' to do hardware multiplication.

[Cyberkuenkuen]

Add a peripheral 'multi3x' to do hardware multiplication. This is the exercise for my semester project.

Changes Made:

Create a directory hw/ip/multi3x/ and add files:

• multi3x.core
• multi3x.sh
• multi3x.vlt
• data/multi3x.hjson
• rtl/multi3x.sv

Modify files:

• hw/core-v-mini-mcu/peripheral_subsystem.sv.tpl (instantiate the multi3x module)
• core-v-mini-mcu.core (declare peripheral package and waiver file)
• mcu_cfg.json (add configuration in the peripherals section)

Run multi3x.sh, which generates:

• rtl/multi3x_reg_pkg.sv
• rtl/multi3x_reg_top.sv
• sw/.../multi3x.h

Create an example app: sw/applications/example_multi3x