[GISel][RISCV] Add irtranslator/legalizer/selector support for G_FREEZE. (#92744)

This patch adds support for G_FREEZE on riscv. It will be selected into
a copy instruction.
 
The ll test is copied from the AArch64 patch:
https://github.com/llvm/llvm-project/commit/665da596854bf07ee25f368855156dde43845013.