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/host_power_off.hpp b/host_power_off.hpp
index 5b8b71f..49231a3 100644
--- a/host_power_off.hpp
+++ b/host_power_off.hpp
@@ -18,6 +18,9 @@
 
 #include <ipmid/api.h>
 
+#include <ipmid/api-types.hpp>
+#include <vector>
+
 namespace google
 {
 namespace ipmi
@@ -25,14 +28,13 @@
 
 struct HostPowerOffRequest
 {
-    uint8_t subcommand;
     // Delay in seconds.
     uint32_t delay;
 } __attribute__((packed));
 
 // Disable the fallback watchdog with given time delay and Power Off Host
-ipmi_ret_t hostPowerOff(const uint8_t* reqBuf, uint8_t* replyBuf,
-                        size_t* dataLen, const HandlerInterface* handler);
+Resp hostPowerOff(const std::vector<std::uint8_t>& data,
+                  const HandlerInterface* handler);
 
 } // namespace ipmi
 } // namespace google