Made passes converting ops from other dialects to spirv OperationPass,
so that downstream compiler could put them in a proper nested pass
manager to lower device code only.
Reviewed By: antiagainst
Differential Revision: https://reviews.llvm.org/D131591
StandardToSPIRV currently contains an assortment of patterns converting from
different dialects to SPIRV. This commit splits up StandardToSPIRV into separate
conversions for each of the dialects involved (some of which already exist).
Differential Revision: https://reviews.llvm.org/D120767