I just tried to boot using the Linux-2.6.18-028test001 you built, and it got a ways into booting, but then died with the following OOPS message:
[ 4.664578] rtc_init: no PC rtc found
[ 5.531306] OOPS: Bogus kernel PC [0000000000000000] in fault handler
[ 6.252782] OOPS: RPC [0000000000474fdc]
[ 6.705507] OOPS: Fault was to vaddr[f7ea4000]
[ 7.220241] Unable to handle kernel NULL pointer dereference
[ 7.826716] tsk->{mm,active_mm}->context = 000000000000010a
[ 8.370634] tsk->{mm,active_mm}->pgd = fffff801fd04e000
[ 8.561620] TRAPLOG: Trap level 1 TSTATE[fffffffffffffffd] TPC[0000000000693c00] TNPC[0000000000000000] TT[1]
[ 8.919896] TRAPLOG: Trap level 2 TSTATE[00000000f7ea4000] TPC[00000000f7ea4000] TNPC[fffff801ff4c8000] TT[80009000]
[ 9.315739] SUN4V-DTLB: Error at TPC[4193b8], tl 8
[ 9.487710] SUN4V-DTLB: vaddr[ffffffffffffe000] ctx[0] pte[800007ffffffe743] error[2]
Program terminated
{3} ok
The first line is normal, and the last line is just the OpenBoot ok prompt. I will go ahead and boot it back into the unpatched 2.6.18 kernel for now and take a look into this as soon as I get a chance.