tools/ocaml/xc: Address ABI issues with physinfo arch flags

tools/ocaml/xc: Address ABI issues with physinfo arch flags

The current bindings function, but the preexisting

  type physinfo_arch_cap_flag =
         | X86 of x86_physinfo_arch_cap_flag

is a special case in the Ocaml type system with an unusual indirection, and
will break when a second option, e.g. `| ARM of ...` is added.

Also, the position the list is logically wrong.  Currently, the types express
a list of elements which might be an x86 flag or an arm flag (and can
intermix), whereas what we actually want is either a list of x86 flags, or a
list of ARM flags (that cannot intermix).

Rework the Ocaml types to avoid the ABI special case and move the list
primitive, and adjust the C bindings to match.

Fixes: 2ce11ce249a3 ("x86/HVM: allow per-domain usage of hardware virtualized APIC")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>