PEL: Point to libpldm repo in subproject

PLDM split into two repositories, so point at the one that is actually
needed as a subproject.  Also remove a PLDM meson option that isn't used
anymore.

Change-Id: I79d4084d9dc6260dc1a0915f679d429f3c81792e
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/extensions/openpower-pels/meson.build b/extensions/openpower-pels/meson.build
index 6a07322..e8fbdd4 100644
--- a/extensions/openpower-pels/meson.build
+++ b/extensions/openpower-pels/meson.build
@@ -1,6 +1,6 @@
 libpldm_dep = dependency(
     'libpldm',
-    default_options: ['libpldm-only=enabled', 'oem-ibm=enabled'],
+    default_options: ['oem-ibm=enabled'],
 )
 
 if cpp.has_header('nlohmann/json.hpp')