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: I794c658531483266bfce6f9b28127a166ed01490
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/libpldmresponder/meson.build b/libpldmresponder/meson.build
index 7de2cf2..f949db9 100644
--- a/libpldmresponder/meson.build
+++ b/libpldmresponder/meson.build
@@ -32,7 +32,7 @@
 
 responder_headers = ['.']
 
-if get_option('oem-ibm').enabled()
+if get_option('oem-ibm').allowed()
    responder_headers += [
     '../oem/ibm/',
    ]
@@ -66,7 +66,7 @@
   include_directories:include_directories(responder_headers),
   link_with: libpldmresponder)
 
-if get_option('tests').enabled()
+if get_option('tests').allowed()
   subdir('test')
 endif