Add header that declares memcpy()

It helps to fix a compilation issue with host libc:

core/fs_mgr/liblp/reader.cpp:252:9: error: use of undeclared identifier 'memcpy'; did you mean 'wmemcpy'?
        memcpy(&partition, cursor, sizeof(partition));
        ^~~~~~
        wmemcpy

Change-Id: I68f9c5b815b09f846aeba67bce0290f6829c80cf
diff --git a/fs_mgr/liblp/reader.cpp b/fs_mgr/liblp/reader.cpp
index dcee6d2..8dbe955 100644
--- a/fs_mgr/liblp/reader.cpp
+++ b/fs_mgr/liblp/reader.cpp
@@ -18,6 +18,7 @@
 
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
 #include <functional>
diff --git a/fs_mgr/liblp/writer.cpp b/fs_mgr/liblp/writer.cpp
index bffcb7e..8a983ad 100644
--- a/fs_mgr/liblp/writer.cpp
+++ b/fs_mgr/liblp/writer.cpp
@@ -17,6 +17,7 @@
 #include "writer.h"
 
 #include <inttypes.h>
+#include <string.h>
 #include <unistd.h>
 
 #include <string>