libpldm: Migrate to subproject

Organize files in libpldm to make it a subproject

In the current state, libpldm is not readily consumable
as a subproject.This commit does all the necessary re-organisation
of the source code to make it work as a subproject.

There are no .c/.h files changes in this commit, only meson
changes and re-organising the code structure.

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: I20a71c0c972b1fd81fb359d604433618799102c6
diff --git a/pldmtool/oem/ibm/oem_ibm_state_set.hpp b/pldmtool/oem/ibm/oem_ibm_state_set.hpp
index d69e2fc..7799c61 100644
--- a/pldmtool/oem/ibm/oem_ibm_state_set.hpp
+++ b/pldmtool/oem/ibm/oem_ibm_state_set.hpp
@@ -1,4 +1,4 @@
-#include "oem/ibm/libpldm/state_set_oem_ibm.h"
+#include "libpldm/state_set_oem_ibm.h"
 
 #include <libpldm/entity.h>
 #include <libpldm/entity_oem_ibm.h>