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: Ia942d083f4ddab68acbbb40699ea1971e09db771
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/cleanup/meson.build b/cleanup/meson.build
index e550064..0e8f031 100644
--- a/cleanup/meson.build
+++ b/cleanup/meson.build
@@ -25,6 +25,6 @@
   install: true,
   install_dir: get_option('libdir') / 'blob-ipmid')
 
-if not get_option('tests').disabled()
+if get_option('tests').allowed()
   subdir('test')
 endif