Add named options

Some of the registers have bits or fields whose values are not boolean
or integers (like 'is present/enabled' or 'number of'), but named
values like the TTMR (disabled, restart, stop, continue). This adds
the corresponding macro defines to the generated or1k-sprs.h.

Example:
<field .. >
  <option name="a" value="0" description="Do it A style" />
  <option name="b" value="1" description="Do it B style" />
</field>