powerpc/64: CONFIG_RELOCATABLE support for hmi interrupts

powerpc/64: CONFIG_RELOCATABLE support for hmi interrupts

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1675806
The branch from hmi_exception_early to hmi_exception_realmode must use
a "relocatable-style" branch, because it is branching from unrelocated
exception code to beyond __end_interrupts.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 2337d207288f163e10bd8d4d7eeb0c1c75046a0c)
Signed-off-by: Breno Leitao <breno.leitao@gmail.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>