[MIPS GlobalISel] Add detailed tests for lower call

Test different operand types of callee and their behavior whether
relocation model is pic or not.
Possible operand types are:
Register (function pointer),
External symbol (used for libcalls e.g. __udivdi3 or memcpy),
Global address.

Global address has different handling depending on relocation model
and linkage type. Register and external symbol do not.

Differential Revision: https://reviews.llvm.org/D62590

llvm-svn: 362212