@colin.stephane - it should be in kernel-power.deb, just wget it and unpack it. though it seems to me that something else broken, I don't know how multiboot works, but aiui flashing a kernel should overwrite it. which you already did.
-bash-2.05b$ uname -a Linux Nokia-N900 2.6.28.10-cssu3 #1 PREEMPT Sat Jul 28 18:05:05 EDT 2012 armv7l GNU/Linux -bash-2.05b$ uptime 16:19:04 up 5 days, 13:20, 0 users, load average: 0.17, 0.27, 0.11 -bash-2.05b$ kernel-config show current kernel configuration: current frequency: 500 supported frequencies: 125 250 500 550 600 720 805 850 900 950 1000 1100 1150 min. frequency: 500 max. frequency: 900 avoid frequencies: 125 active frequencies: 250:25,180 500:37,360 550:40,400 600:42,430 720:47,430 805:51,430 850:53,500 900:56,500 950:60,500 1000:60,500 1100:72,520 1150:72,520 SmartReflex VDD1=1, VDD2=1 governor ondemand: ignore nice load= 0, up threshold= 70, sampling rate= 300000, powersave bias= 20 -bash-2.05b$