CVE-2022-50870 powerpc/rtas: avoid device tree lookups in rtas_os_term()

In the Linux kernel, the following vulnerability has been resolved: powerpc/rtas: avoid device tree lookups in rtasosterm rtasosterm is called during panic. Its behavior depends on a couple of conditions in the /rtas node of the device tree, the traversal of which entails locking and local IRQ...