build: use allowed over enabled

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`.

Change-Id: I4db060ea85cfae7be96693ec04a09829767351a1
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/test/meson.build b/test/meson.build
index 29d4b95..300e977 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -13,7 +13,7 @@
         gmock_dep = gtest_proj.dependency('gmock')
   else
         assert(
-            not get_option('tests').enabled(),
+            not get_option('tests').allowed(),
             'Googletest is required if tests are enabled'
         )
   endif
@@ -28,7 +28,7 @@
   'utest.cpp',
   'utest-led-json.cpp',
 ]
-if get_option('persistent-led-asserted').enabled()
+if get_option('persistent-led-asserted').allowed()
   test_sources += [
     '../manager/serialize.cpp',
   ]