build: use allowed over enabled or not-disabled

Meson feature options are typically in a tri-state of enabled, disabled,
or auto.  The enabled and disabled functions on an option (from
`get_option`) no longer return true for auto features.  Instead, the
expectation is to use `allowed()` which is true for both enabled and
auto.

Switch all uses of `enabled` to `allowed`.
Switch all uses of `not disabled` to `allowed`.

Change-Id: Ic3591e9228286b3e98ef043638ca8e110e58f1d3
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meson.build b/meson.build
index 17232b1..9b87a3d 100644
--- a/meson.build
+++ b/meson.build
@@ -240,7 +240,7 @@
     'dbus/org.open_power.Software.Host.Updater.conf',
     install_dir: dbus_policy_dir)
 
-if not get_option('tests').disabled()
+if get_option('tests').allowed()
     oe_sdk = get_option('oe-sdk')
     if oe_sdk.allowed()
         # Setup OE SYSROOT