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: I2f446393dfb207d1429ec4a3a0c6b66f23e30ec7
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meson.build b/meson.build
index 4f0e3c6..269ec49 100644
--- a/meson.build
+++ b/meson.build
@@ -108,7 +108,7 @@
 
 no_listener_mode = get_option('nlmode')
 
-if not no_listener_mode.disabled()
+if no_listener_mode.allowed()
     executable(
         'openpower-hw-diags',
         sources: ['main_nl.cpp', 'cli.cpp', buildinfo, plugins_src],
@@ -138,7 +138,7 @@
 
 build_tests = get_option('tests')
 
-if not build_tests.disabled()
+if build_tests.allowed()
 
     # IMPORTANT NOTE:
     # We cannot link the test executables to `util_lib` because: