build: meson support for openpower-pel extensions

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I4b45f71a3de4966fe3649480d4333806f201f405
diff --git a/extensions/meson.build b/extensions/meson.build
new file mode 100644
index 0000000..8773dc4
--- /dev/null
+++ b/extensions/meson.build
@@ -0,0 +1,3 @@
+if not get_option('openpower-pel-extension').disabled()
+    subdir('openpower-pels')
+endif