[AMDGPU] Handle functions in llvm's global ctors and dtors list

This patch introduces a new code object metadata field, ".kind"
which is used to add support for init and fini kernels.

HSAStreamer will use function attributes, "device-init" and
"device-fini" to distinguish between init and fini kernels from
the regular kernels and will emit metadata with ".kind" set to
"init" and "fini" respectively.

To reduce the number of init and fini kernels, the ctors and
dtors present in the llvm's global.ctors and global.dtors lists
are called from a single init and fini kernel respectively.

Reviewed by: yaxunl

Differential Revision: https://reviews.llvm.org/D105682