libpldm: change header install path

Install headers to $(includedir)/libpldm instead of $(includedir). This
is considered an autoconf best practice.

Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
Change-Id: I5c84f0b13da58531e6cf5e6967910ec5a0517dd6
diff --git a/libpldm/Makefile.am b/libpldm/Makefile.am
index 821f390..e37b639 100644
--- a/libpldm/Makefile.am
+++ b/libpldm/Makefile.am
@@ -1,4 +1,5 @@
-nobase_include_HEADERS = \
+libpldm_includedir = $(includedir)/libpldm
+libpldm_include_HEADERS = \
 	base.h \
 	pldm_types.h \
 	platform.h \