[llvm] [RISCV][docs] GP Relaxation and Small Data Limit (PR #108592)

[Sam Elliott via llvm-commits]

lenary wrote:

Oh also, I have not documented what the default actually is for this, because I'm not sure it is agreed. I've also not documented non-llvm tools/libraries.

https://github.com/llvm/llvm-project/pull/108592