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