[AMDGPU] Add disassembler diagnostics for invalid kernel descriptors (#87400)

These mostly are checking for various reserved bits being set. The diagnostics
for gpu-dependent reserved bits have a

[AMDGPU] Add disassembler diagnostics for invalid kernel descriptors (#87400)

These mostly are checking for various reserved bits being set. The diagnostics
for gpu-dependent reserved bits have a bit more context since they seem like the
most likely ones to be observed in practice.

This commit also improves the error handling mechanism for
MCDisassembler::onSymbolStart(). Previously it had a comment stream parameter
that was just being ignored by llvm-objdump, now it returns errors using
Expected<T>.

show more ...