Buildroot boot fails on QEMU

[jordancarlin]

The new buildroot configuration boots successfully in lockstep on Wally, but fails in QEMU. It gets through the OpenSBI boot and all associated messages, but hangs before any messages from the kernel start. It seems to be related to the Svpbmt extension, removing it from the device tree results in a successful boot.

Need to investigate if there is a way to enable this extension in QEMU or if it is just not supported. Would also be good to disable hypervisor and sdtrig extensions in QEMU to make it more closely match Wally.