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: I2253ebff36b49c4b79b803175dd76668f8ac2ba8
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/attn/meson.build b/attn/meson.build
index 5a2834b..b1f0d9e 100644
--- a/attn/meson.build
+++ b/attn/meson.build
@@ -10,7 +10,7 @@
 attn_conf = configuration_data()
 
 # conditionally define ENABLE_PHAL_TRUE
-if (get_option('phal').enabled())
+if (get_option('phal').allowed())
     attn_conf.set('ENABLE_PHAL_TRUE', '')
 else
     attn_conf.set('ENABLE_PHAL_TRUE', '#')
@@ -71,7 +71,7 @@
 ]
 
 # conditional library dependencies
-if get_option('phal').enabled()
+if get_option('phal').allowed()
   attn_deps += libphal_dep
 endif