Implement RISC-V Zb extension intrinsics

Author: coastalwhite

crates/core_arch/src/riscv64/mod.rs

@@ -1,8 +1,10 @@
 //! RISC-V RV64 specific intrinsics
 use crate::arch::asm;
 
+mod zb;
 mod zk;
 
+pub use zb::*;
 pub use zk::*;
 
 /// Loads virtual machine memory by unsigned word integer