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/.gitignore b/.gitignore
index 8ad1400..516b46f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 subprojects/*
+!subprojects/libpldm*
 !subprojects/*.wrap
 
 # Template from