[PowerPC][NFC] Testing ROTL of v1i128.

Summary: A bug is reported in bugzilla-45628, where the swap_with_shift case can’t be matched to a single HW instruction xxswapd as expected. In fact the case matches the idiom of rotate, but PPC doesn’t support ROTL v1i128.
This is a NFC patch for testing ROTL with v1i128 at master.

Reviewed By: steven.zhang

Differential Revision: https://reviews.llvm.org/D81073