Implement starter-pack instructions for RISCOF framework

[TheDeepestSpace]

We need a couple of instructions before we can run the RISCOF arch-test quite, specifically:

• addi @DanielTaoHuang123 (add sw_testbench #50)
• auipc @DanielTaoHuang123 / @houjingl
• li @DanielTaoHuang123
• lui @houjingl
• srli @MM871 / @DanielTaoHuang123 (add testbench for srli instruction #54)
• nop @MM871 / @TheDeepestSpace
• or @TheDeepestSpace (Add testbench for or instruction #48)

[DanielTaoHuang123]

need to implement the immext; important for aui