Buildbot needs configuration? powerpc_8540 is now powerpc_8548 ?

[Hannu Nyman]

Apparently the mpc85xx CPU type was changed from 8540 to 8548 on 29 Dec 2022, 
causing the package architecture to be powerpc_8548 instead of powerpc_8540, 
but noboby informed the packages buildbot, so it is still trying to churn 
powerpc_8540 and naturally fails :-(

PR:   https://github.com/openwrt/openwrt/pull/11629
commit: 
https://github.com/openwrt/openwrt/commit/2cad88b99fdae9766de84e6c1cb56f111eb53748

Buildbot status for powerpc_8540: 
https://buildbot.openwrt.org/master/packages/#/builders/14

Forum discussion: 
https://forum.openwrt.org/t/opkg-update-fails-with-wget-error-8-repository-folder-missing-powerpc-8548/148425


Visible also at the master snapsts packages download site:

https://downloads.openwrt.org/snapshots/packages/

mipsel_mips32/    -    Fri Jan 13 08:44:11 2023
powerpc_464fp/    -    Sat Jan 14 02:22:42 2023
powerpc_8540/    -    Fri Dec 30 06:18:13 2022
x86_64/    -    Sun Jan 15 11:44:24 2023