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: I1fb38a8715c8dbec883beaadd8519472de452e43
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meson.build b/meson.build
index b317d1a..715045c 100644
--- a/meson.build
+++ b/meson.build
@@ -27,7 +27,7 @@
 
 snoopd_src = ['main.cpp']
 snoopd_args = ''
-if get_option('snoop').enabled()
+if get_option('snoop').allowed()
   snoopd_src += 'ipmisnoop/ipmisnoop.cpp'
   add_project_arguments('-DENABLE_IPMI_SNOOP',language:'cpp')
   snoopd_args += ' -h "' + get_option('host-instances') + '"'