The 'CONFIG_' prefix is not implicit in IS_ENABLED().
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>