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: I8671a81c57e5032c776691d30a941c19b1d53e9d
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/host-transport-extensions/pldm/meson.build b/host-transport-extensions/pldm/meson.build
index fc4c143..54f75ff 100644
--- a/host-transport-extensions/pldm/meson.build
+++ b/host-transport-extensions/pldm/meson.build
@@ -6,7 +6,7 @@
 
 phosphor_dump_manager_dependency += [ dependency('libpldm') ]
 
-if get_option('openpower-dumps-extension').enabled()
+if get_option('openpower-dumps-extension').allowed()
     subdir('oem/ibm')
 else
     subdir('default')