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/pldmtool/meson.build b/pldmtool/meson.build
index 765bdba..17fe374 100644
--- a/pldmtool/meson.build
+++ b/pldmtool/meson.build
@@ -10,7 +10,7 @@
   'pldmtool.cpp',
 ]
 
-if get_option('oem-ibm').enabled()
+if get_option('oem-ibm').allowed()
 sources += [
     'oem/ibm/pldm_oem_ibm.cpp',
   ]