ima: fix build error

IMA_LSM_RULES requires AUDIT.  This is automatic if SECURITY_SELINUX=y
but not when SECURITY_SMACK=y (and SECURITY_SELINUX=n), so make the
dependency explicit.  This fixes the following build error:

security/integrity/ima/ima_policy.c:111:error: implicit declaration of function 'security_audit_rule_match'
security/integrity/ima/ima_policy.c:230:error: implicit declaration of function 'security_audit_rule_init'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>