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: I8a8a5b86aaeb9ae6835ca26b22a8e21e4438bb52
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meson.build b/meson.build
index c454225..dd02612 100644
--- a/meson.build
+++ b/meson.build
@@ -19,7 +19,7 @@
 conf_data.set('MAX_BOOT_CYCLE_COUNT',get_option('max-boot-cycle-count'))
 conf_data.set('MAX_POST_CODE_SIZE_PER_CYCLE',get_option('max-post-code-size-per-cycle'))
 
-if get_option('bios-post-code-log').enabled()
+if get_option('bios-post-code-log').allowed()
   add_project_arguments('-DENABLE_BIOS_POST_CODE_LOG',language: 'cpp')
 endif