pldmtool: oem: ibm: add missing header

Add a missing include of libpldm/entity.h for PLDM_ENTITY enumerations.

Change-Id: I08b03d98185e5dc18c42a24242064e198f56c597
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/pldmtool/oem/ibm/oem_ibm_state_set.hpp b/pldmtool/oem/ibm/oem_ibm_state_set.hpp
index 27cb21b..6f9468f 100644
--- a/pldmtool/oem/ibm/oem_ibm_state_set.hpp
+++ b/pldmtool/oem/ibm/oem_ibm_state_set.hpp
@@ -2,6 +2,8 @@
 
 #include "oem/ibm/libpldmresponder/oem_ibm_handler.hpp"
 
+#include <libpldm/entity.h>
+
 /** @brief PLDM OEM State Set range as per DSP0249_1.1.0 specification
  */
 enum pldm_oem_state_set_id_codes