The MPU is an implementation option available for both ARMv6-M and ARMv7-M.
Remove poorly merged code that attempted to include this only for cortex m0+.
Added doxygen, updated the definitions of the RBAR register, (though if you're
really using this periperhal, you should be looking at the ref man for further
information)
Reported-by: forrestv on irc.
f4d6da9554