[C-extension] Collect statistics of instructions that may directly map to C-extension instructions

[penguinwu]

Augment the trace analysis tool to collect statistics on instructions that can be directly rewritten into C-extension instructions.

Those that can be rewritten to C-extension instructions need to satisfy additional constraints such as:

• the immediate or address offset is small, or
• one of the registers is the zero register (x0), the ABI link register (x1), or the ABI stack pointer (x2), or
• the destination register and the first source register are identical, or
• the registers used are the 8 most popular ones

Report the percentage of instructions (for each regular instruction) that can be rewritten to C-extension instructions (i.e., 40% of add can be rewritten to C-extension add

[penguinwu]

Not sure if @LOGQTAINIA or @luyahan is better suited for this issue. I'll let you two decide

[ghost]

Migrated to v8-riscv/v8-riscv-tools#2