selftests/kexec: Add missing '=y' to config options

so the file can be used as kernel config snippet.

Signed-off-by: Petr Vorel <[e-mail]>
[[e-mail]: remove CONFIG_KEXEC_VERIFY_SIG from config]
Signed-off-by: Mimi Zohar <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/kexec/config

···
-CONFIG_IMA_APPRAISE
-CONFIG_IMA_ARCH_POLICY
-CONFIG_SECURITYFS
-CONFIG_KEXEC_VERIFY_SIG
+CONFIG_IMA_APPRAISE=y
+CONFIG_IMA_ARCH_POLICY=y
+CONFIG_SECURITYFS=y