build: enable adding MbedTLS files for platform

The platform.mk can add extra MbedTLS source files to LIBMBEDTLS_SRC.

Change-Id: Ida9abfd59d8b02eae23ec0a7f326db060b42bf49
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
1 file changed