I have other things to do so I won't be able to finish today.  In case
someone wants to work on this over the weekend, attached is a patch of
what I have so far.  It implements the example bi_rec's emailed before
for the ev64260 board.  Feel free to use it or do a better job.

Comments:
1) I added 2 new routines to arch/ppc/kernel/setup.c:
- find_bi_rec() searches that level of bi_rec's for the specified tag
(i.e., it does not scan nested ones)
- find_bi_rec_dev() searches that level for a BI_DEVICE bi_rec that has
bi_rec's nested inside it with the specified BI_DEV_TYPE and BI_DEV_ID.
It returns a ptr to the first bi_rec inside that BI_DEVICE bi_rec that
matches.  Is there a better place than setup.c for these routines?

2) Each routine takes a bi_rec as a starting point so you can use the
same routine by simply adding bi_rec->size to your bi_rec ptr that was
returned and call that routine again.

3) I didn't bother changing parse_bootinfo() to use find_bi_rec()
because there was no point.

4) I modified arch/ppc/boot/common/misc-simple.c:decompress_kernel() to
call add_extra_bi_recs().  A stub for that routine is in
arch/ppc/boot/simple/bi_rec-stub.c for all boards excepts ones with
CONFIG_GT64260 defined (in which case, the routine is in
arch/ppc/boot/simple/bi_rec-gt64260.c).  As others want to add bi_rec's
in the linuxppc bootloader, they can make their own version of that
routine.

4) I don't have hardware so none of this code has been tested.

Mark