selftests/efivarfs: add required kernel configs

add config file

Signed-off-by: Lei Yang <Lei.Yang@windriver.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/efivarfs/config

@@ -0,0 +1 @@
+CONFIG_EFIVAR_FS=y