[Flang] Replace intrinsic function type generators with single generic function type generator

In a future patch we plan on introducing a large set of Power-PC specific intrinsics. During our prototyping we found that the number of function type generators we were defining, plus those already defined, were reaching an unreasonable number. This patch introduces a generic function type generator function that can be used for almost all cases. The generator supports creating function types with up to 4 arguments and with arguments/return type of types: void, integer, real, and comlex. The intention is for a future patch, which introduces a set of PowerPC-specific vector intrinsics, to also introduce support in the generator for: integer vector, unsigned vector, and real vector types.

Reviewed By: luporl

Differential Revision: https://reviews.llvm.org/D151812