powerpc/8xx: Remove now unused TLB miss functions

The code to setup linear and IMMR mapping via huge TLB entries is
not called anymore. Remove it.

Also remove the handling of removed code exits in the perf driver.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/75750d25849cb8e73ca519866bb892d7eb9649c0.1589866984.git.christophe.leroy@csgroup.eu