[PowerPC] add store (load float*) pattern to isProfitableToHoist

store (load float*) can be optimized to store(load i32*) in InstCombine pass.

Add store (load float*) to isProfitableToHoist to make sure we don't break
the opt in InstCombine pass.

Reviewed By: jsji

Differential Revision: https://reviews.llvm.org/D82341