Module signing and dm-verity needs key pair to be generated
using openssl. Add keygen file which is needed to generate
keys using openssl.
Change-Id: Ib3b11c50029e5f58c7b3c3a98cfdefb0c45a7d2b
Signed-off-by: Keerthi Gowda Balehalli Satyanarayana <kbalehal@codeaurora.org>