[llvm] [RISCV][GISEL] Do not initialize GlobalISel objects unless needed (PR #98233)

[Craig Topper via llvm-commits]

topperc wrote:

> This helps since the constructors of the GlobalISel objects have a significant amount of code.

Only RISCVLegalizerInfo has any significant code as far as I can tell?

https://github.com/llvm/llvm-project/pull/98233