Add Raspberry Pi automatic environment setup

Patch by derhass.

Requested at
<http://www.dxx-rebirth.com/frm/index.php/topic,1048.msg17426/topicseen.html#msg17426>.
Make GET_INTEL_* const-correct

Based on a report by derhass, but with additional changes.  Original
report at

<http://www.dxx-rebirth.com/frm/index.php/topic,1048.msg17421.html#msg17421>.