pldmtool: oem: ibm: untangle header dependencies

With the oem-ibm meson option enabled, pldm_platform_command.cpp has the
following header dependency chain:

requester/handler.hpp
host-bmc/dbus_to_event_handler.hpp
libpldmresponder/platform.hpp
oem/ibm/libpldmresponder/inband_code_update.hpp
oem/ibm/libpldmresponder/oem_ibm_handler.hpp
pldmtool/oem/ibm/oem_ibm_state_set.hpp
pldmtool/pldm_platform_cmd.cpp

requester/handler.hpp has a dependency on sd_event.  Since sd_event is
not listed as a dependency of pldmtool, this results in a compile
failure when building in subproject mode.

Clearly it isn't appropriate to add sd_event as a pldmtool dependency.
To fix the compile failure, break the include dependency chain between
oem_ibm_state_set.hpp and oem_ibm_handler.hpp.  This is likely an
intra-pldm domain violation anyway (pldmtool <-> libpldmresponder).

oem_ibm_state_set.hpp includes oem_ibm_handler.hpp to make use of a
single constant: PLDM_OEM_IBM_ENTITY_FIRMWARE_UPDATE.  To break the
dependency chain, PLDM_OEM_IBM_ENTITY_FIRMWARE_UPDATE is moved to an oem
version of entity.h.

Change-Id: I2b54ad9a7559ecf5fbe01c6a52a24428e56df77e
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/oem/ibm/libpldmresponder/oem_ibm_handler.cpp b/oem/ibm/libpldmresponder/oem_ibm_handler.cpp
index 138ef01..efa4790 100644
--- a/oem/ibm/libpldmresponder/oem_ibm_handler.cpp
+++ b/oem/ibm/libpldmresponder/oem_ibm_handler.cpp
@@ -7,6 +7,8 @@
 #include "libpldmresponder/file_io.hpp"
 #include "libpldmresponder/pdr_utils.hpp"
 
+#include <libpldm/entity_oem_ibm.h>
+
 using namespace pldm::pdr;
 using namespace pldm::utils;