[llvm] [RISCV] Set the reciprocal throughtput cost for division to TTI::TCC_Expensive (PR #177516)

[Ryan Buchner via llvm-commits]

bababuck wrote:

Also @lukel97, I noticed that when you commit your own PRs the email in the git log is listed as `luke at igalia.com`, but when you've modified a PR, the automated Github merge message lists your information as `Co-authored-by: Luke Lau <luke_lau at icloud.com>`. Not sure if that's intentional or not.

https://github.com/llvm/llvm-project/pull/177516