Add IPMI OEM command LinuxBootDone

Add a new OEM command for LinuxBoot to notify the BMC when it is about
to kexec into the OS. This is intended to give the BMC a chance to
prepare for an untrusted OS, e.g. disable any interfaces it doesn't want
the OS to have access to.

Tested:
Exercised the new OEM command using ipmitool
$ ipmitool raw 0x2e 0x32 0x79 0x2b 0x00 0x11
  79 2b 00 11

Change-Id: Ica76d77cdde48cebfbced32d8e7e860b559074e8
Signed-off-by: John Wedig <johnwedig@google.com>
diff --git a/handler_impl.hpp b/handler_impl.hpp
index bad01f1..5d74435 100644
--- a/handler_impl.hpp
+++ b/handler_impl.hpp
@@ -70,6 +70,7 @@
                           uint8_t num_bytes) const override;
     void accelOobWrite(std::string_view name, uint64_t address,
                        uint8_t num_bytes, uint64_t data) const override;
+    void linuxBootDone() const override;
 
   protected:
     // Exposed for dependency injection