CVE-2023-52606

In the Linux kernel, the following vulnerability has been resolved:

powerpc/lib: Validate size for vector operations

Some of the fp/vmx code in sstep.c assume a certain maximum size for the
instructions being emulated. The size of those operations however is
determined separately in analyse_instr().

Add a check to validate the assumption on the maximum size of the
operations, so as to prevent any unintended kernel stack corruption.