[llvm] [RISCV] Replace HasStdExtZbcOrZbkc with HasStdExtZbkc. NFC (PR #185790)

[Craig Topper via llvm-commits]

topperc wrote:

> Why don't we want to change the assembler errors?

I figure some people may be more familiar with Zbc than Zbkc. Zbc is mentioned as optional extension in the RVA23 profile for example. If we print both, then maybe the user can decide which one they want instead of adding Zbkc to their command line, and then finding out later they really meant Zbc because they also want to use clmulr.

https://github.com/llvm/llvm-project/pull/185790