[PowerPC] Fix td pattern for P10 VSLDBI and VSRDBI
This patch fixes the pattern for the P10 instructions Vector Shift Left
Double by Bit Immediate VN-form and Vector Shift Right Double by Bit
Immediate VN-form. The third argument should be a target constant (timm)
instead of an i32 because an immediate is expected.
Reviewed By: lei
Differential Revision: https://reviews.llvm.org/D109920