[RISCV] Handle PseudoVRELOAD and PseudoVSPILL in getInstSizeInBytes.

It's necessary to calculate correct instruction size because
PseudoVRELOAD and PseudoSPILL will be expanded into multiple
instructions.

Reviewed By: frasercrmck

Differential Revision: https://reviews.llvm.org/D100702