build: meson support for openpower-pel extensions

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4b45f71a3de4966fe3649480d4333806f201f405
diff --git a/config.h.meson b/config.h.meson
index 1b33374..bafd142 100644
--- a/config.h.meson
+++ b/config.h.meson
@@ -26,8 +26,10 @@
 
 #ifdef TESTCASE
 #define ERRLOG_PERSIST_PATH "/tmp/errors"
+#define EXTENSION_PERSIST_DIR "/tmp/extensions"
 #else
 #define ERRLOG_PERSIST_PATH "/var/lib/phosphor-logging/errors"
+#define EXTENSION_PERSIST_DIR "/var/lib/phosphor-logging/extensions"
 #endif
 
 static constexpr size_t ERROR_CAP = @error_cap@;