google-ipmi-sys: Refactor to use new version of OEM IPMI Handler

Using the new version of ipmi handler provide a higher level wrapper
over the same functionalities. It helps us parse the input and output to
have more control of the input/output we see.

The input and output will be
`std::uint8_t, std::optional<std::vector<uint8_t>>`.

This represents `subcommand` and any input data.

Changes to note,
- all subcommand in the request/response struct are removed. It will be
  managed by the wrapper directly.
    - Unit tests checking for input with only the subcommand are
      removed.
- Move all reply struct to header files to be accessible in unit test.

Tested:
All IPMI OEM command still works the same as before this change.

Change-Id: I4230ab84a497a867248fe82224e32cc69b314b64
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/handler.hpp b/handler.hpp
index e0d73d7..26950e9 100644
--- a/handler.hpp
+++ b/handler.hpp
@@ -15,7 +15,9 @@
 #pragma once
 
 #include <cstdint>
+#include <ipmid/api-types.hpp>
 #include <map>
+#include <span>
 #include <string>
 #include <tuple>
 #include <vector>
@@ -25,6 +27,8 @@
 namespace ipmi
 {
 
+using Resp = ::ipmi::RspType<std::uint8_t, std::vector<uint8_t>>;
+
 using VersionTuple =
     std::tuple<std::uint8_t, std::uint8_t, std::uint8_t, std::uint8_t>;