powerpc: Remove unreachable relocation on exception handlers

We have relocation on exception handlers defined for h_data_storage and
h_instr_storage. However we will never take relocation on exceptions for
these because they can only come from a guest, and we never take
relocation on exceptions when we transition from guest to host.

We also have a handler for hmi_exception (Hypervisor Maintenance) which
is defined in the architecture to never be delivered with relocation on,
see see v2.07 Book III-S section 6.5.

So remove the handlers, leaving a branch to self just to be double extra
paranoid.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
CC: <stable@vger.kernel.org> [v3.9+]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>