crypto: drbg - Use Kconfig to ensure at least one RNG option is set

crypto: drbg - Use Kconfig to ensure at least one RNG option is set

This patch removes the build-time test that ensures at least one RNG
is set.  Instead we will simply not build drbg if no options are set
through Kconfig.

This also fixes a typo in the name of the Kconfig option CRYTPO_DRBG
(should be CRYPTO_DRBG).

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>