[mlir][spirv] De-template deserialization

Previously for each op we generate a separate deserialization
method for it. Those deserialization methods duplicate the logic
of parsing operands/results/attributes and such.

This commit creates a generic method and let suitable op-specific
deserialization method to call into it.

wc -l SPIRVSerialization.inc: before 13290; after: 8304 (So -4986)

Reviewed By: hanchung, ThomasRaoux

Differential Revision: https://reviews.llvm.org/D93504