RISC-V: Update implication from zbc

rust-lang/rust#140139 changed the target feature implication without
updating the Reference.

This commit fixes this issue.

Author: a4lg

src/attributes/codegen.md

@@ -432,7 +432,7 @@ Feature     | Implicitly Enables  | Description
 `c`         |                     | [C][rv-c] --- Compressed instructions
 `m`         |                     | [M][rv-m] --- Integer Multiplication and Division instructions
 `zba`       |                     | [Zba][rv-zba] --- Address Generation instructions
-`zbb`       |                     | [Zbb][rv-zbb] --- Basic bit-manipulation
+`zbb`       | `zbkc`              | [Zbb][rv-zbb] --- Basic bit-manipulation
 `zbc`       |                     | [Zbc][rv-zbc] --- Carry-less multiplication
 `zbkb`      |                     | [Zbkb][rv-zbkb] --- Bit Manipulation Instructions for Cryptography
 `zbkc`      |                     | [Zbkc][rv-zbc] --- Carry-less multiplication for Cryptography