[llvm] [RISCV][GISel] Add ISel supports for SHXADD from Zba extension (PR #67863)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

Note that this patch depends on #68125 so the buildbot failures in this patch are expected.

https://github.com/llvm/llvm-project/pull/67863