In CP0 Index register, bit 31 means 'Probe Failure', while lowest bits
contain the TLB index.

In tlbwi and tlbwr instructions, this Probe Failure bit must be ignored
when reading the TLB index.

Attached patch fixes it.

(Hervé Poussineau)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5215 c046a42c-6fe2-441c-8c8c-71466251a162