evm: enable key retention service automatically

If keys are not enabled, EVM is not visible in the configuration menu.
It may be difficult to figure out what to do unless you really know.
Other subsystems as NFS, CIFS select keys automatically. This patch does
the same.

This patch also removes '(TRUSTED_KEYS=y || TRUSTED_KEYS=n)' dependency,
which is unnecessary. EVM does not depend on trusted keys, but on
encrypted keys. evm.h provides compile time dependency.
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/evm/Kconfig

 config EVM
 	boolean "EVM support"
-	depends on SECURITY && KEYS && (TRUSTED_KEYS=y || TRUSTED_KEYS=n)
+	depends on SECURITY
+	select KEYS
+	select ENCRYPTED_KEYS
 	select CRYPTO_HMAC
 	select CRYPTO_SHA1
-	select ENCRYPTED_KEYS
 	default n
 	help
 	  EVM protects a file's security extended attributes against