I do know that setting Env variable OPENSSL_FIPS=1 will turn on FIPS mode for openssl/sshd binary.
Now, Is there a way to turn on FIPS mode for all the applications(SSH, Apache Server etc) which uses libcrypto using a single switch? Or in other words, how to make libcryto to work in FIPS mode?
You have to do it from each application. openssl is an application that statically links the crypto libraries. Even if you used the dynamic crypto libraries (so or dll depending on your platform). you still have to set it. Look at the FIPS_140-2-opensslUserGuide. There are a couple version out there, but all have the basic question you are asking. Also, make sure you read the FIPS_1402-opensslSecurityPolicy document.
Last, you may find this link helpful for testing and validating: