* https://github.com/riscv/riscv-b/tags
Added standard B extension back, which implies Zba, Zbb and Zbs extensions.
* https://github.com/riscv/riscv-zaamo-zalrsc/tags
Splited standard A extension into two new extensions, Zaamo and Zalrsc.
The A extension implies Zaamo and Zalrsc extensions.
Not sure if we need to do the similar check as i and zicsr/zifencei.