openrisc: Remove unused IMMU tlb workardound

This looks to be some historical code that was used to convert TLB
misses on branches from l.bf, l.jal, l.j etc all to a trampoline
using l.jr (jump register).  I don't see this being used and I don't
know the history of it so remove it.

Signed-off-by: Stafford Horne <shorne@gmail.com>