[OCaml] Add missing TypeKinds, Opcode, and AtomicRMWBinOps

There are several enum values that have been added to LLVM-C that are
missing from the OCaml bindings. The types defined in
bindings/ocaml/llvm/llvm.ml should be in sync with the corresponding
enum definitions in include/llvm-c/Core.h. The enum values are passed
from C to OCaml unmodified, and clients of the OCaml bindings
interpret them as tags of the corresponding OCaml types. So the only
changes needed are to add the missing constructors to the type
definitions, and to change the name of the maximum opcode in an
assertion.

Differential Revision: https://reviews.llvm.org/D98578