resulting from feedback.
move multiple copies of code for parsing boot.cfg file from sparc, i386
and zaurus into libsa/bootcfg.{h,c}. largely retained i386 parsing logic
in addition to keeping sparc dispatch function while remaining consistent
with boot.cfg(5).
previous sparc64 file format has been obsoleted but only used by boot
CDs distrib/sparc64/bootfs/boot.cfg has been updated to compensate.
exported names have been prefixed with either BOOTCFG_ or bootcfg_ as per
feedback from christos@
tested on amd64 & sparc64 but not zaurus.
e9c95bf579