[AMDGPU] Pass to propagate ABI attributes from kernels to the functions

The pass works in two modes:

Mode 1: Just set attributes starting from kernels. This can work at
the very beginning of opt and llc pipeline, but cannot clone functions
because it must be a function pass.

Mode 2: Actually clone functions for new attributes. This can only work
after all function passes in the opt pipeline because it has to be a
module pass.

Differential Revision: https://reviews.llvm.org/D63208

llvm-svn: 363586