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: I2c043f5e8daae2f0c603a091f707ce06b1c7663e
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/extensions/openpower-pels/meson.build b/extensions/openpower-pels/meson.build
index f1c10f1..478a83c 100644
--- a/extensions/openpower-pels/meson.build
+++ b/extensions/openpower-pels/meson.build
@@ -19,7 +19,7 @@
 extra_dependencies = []
 extra_args = []
 
-build_phal = get_option('phal').enabled()
+build_phal = get_option('phal').allowed()
 
 if build_phal
     extra_sources += [