meson: Reduce strength of oem-ibm requirements from enabled to allowed

If it's not expressly disabled, do what's necessary to build the oem-ibm
pieces of the code-base. Capture the newly-enabled APIs in the ABI
dumps.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I50168309432620e03f00a4620b6bfc38f2e575c8
diff --git a/include/libpldm/meson.build b/include/libpldm/meson.build
index 92a5e9b..4ff250c 100644
--- a/include/libpldm/meson.build
+++ b/include/libpldm/meson.build
@@ -23,7 +23,7 @@
   'transport/mctp-demux.h'
 )
 
-if get_option('oem-ibm').enabled()
+if get_option('oem-ibm').allowed()
   libpldm_include_dir += include_directories('oem/ibm')
   libpldm_headers += files(
     'oem/ibm/libpldm/entity_oem_ibm.h',