Add fir subdir to Axone mss HWP compile path

Some new HWPs are coming so need to pull in more directories.

Change-Id: I7fe01a1a65bc0a47f03f25596f39bc071fbd5b85
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/89853
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>

src/usr/isteps/mss/makefile

@@ -5,7 +5,7 @@
 #
 # OpenPOWER HostBoot Project
 #
-# Contributors Listed Below - COPYRIGHT 2016,2019
+# Contributors Listed Below - COPYRIGHT 2016,2020
 # [+] International Business Machines Corp.
 #
 #
@@ -75,6 +75,7 @@ MSS_LIB += ${AXONE_PROCEDURES_PATH}/hwp/memory/lib/eff_config/
 MSS_LIB += ${AXONE_PROCEDURES_PATH}/hwp/memory/lib/utils/
 MSS_LIB += ${AXONE_PROCEDURES_PATH}/hwp/memory/lib/freq/
 MSS_LIB += ${AXONE_PROCEDURES_PATH}/hwp/memory/lib/workarounds/
+MSS_LIB += ${AXONE_PROCEDURES_PATH}/hwp/memory/lib/fir/
 MSS_LIB += ${EXPLORER_PROCEDURES_PATH}/hwp/memory/
 MSS_LIB += ${EXPLORER_PROCEDURES_PATH}/hwp/memory/lib/
 MSS_LIB += ${EXPLORER_PROCEDURES_PATH}/hwp/memory/lib/eff_config/