[llvm-c][Disassembler] Add an option to print latency information in
disassembled output alongside the instructions.
E.g., on a vector shuffle operation with a memory operand, disassembled
outputs are:
* Without the option:
    vpshufd $-0x79, (%rsp), %xmm0

* With the option:
    vpshufd $-0x79, (%rsp), %xmm0   ## Latency: 5

The printed latency is extracted from the schedule model available in the
disassembler context. Thus, this option has no effect if there is not a
scheduling model for the target.
This boils down to one may need to specify the CPU string, so that this
option could have an effect.

Note: Latency < 2 are not printed.

This part of <rdar://problem/14687488>.