From: Valdis.Kletnieks@vt.edu

15 changes of #if to #ifdef and 2 places CONFIG_FOO should be
defined(CONFIG_FOO).  This gets rid of spurious warnings if you build with
"-Wundef" so you get a warning if you have a preprocessor command like:

#if CONFIG_ETRAX_DS1302_RSTBIT == 27

and you'll be told if it's substituting a zero rather than silent
weirdness and unexpected code generation.