selftests/powerpc: Adjust wild_bctr to build with old binutils

Currently the selftest wild_bctr can fail to build when an old gcc is
used, notably on gcc using a binutils version <= 2.27, because the
assembler does not support the integer suffix UL.

This patch adjusts the wild_bctr test so the REG_POISON value is still
treated as an unsigned long for the shifts on compilation but the UL
suffix is absent on the stringification, so the inline asm code
generated has no UL suffixes.

Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>
[mpe: Wrap long line]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

selftests/powerpc: Fix wild_bctr test to work on ppc64

The selftest I recently added to test branching to an out-of-bounds
NIP doesn't work on 64-bit big endian. It does fail but not in the
right way. That is it SEGVs trying to load from the opd at BAD_NIP,
but it never gets as far as branching to BAD_NIP.

To fix it we need to create an opd which is reachable but which holds
the bad address.

Fixes: b7683fc66eba ("selftests/powerpc: Add a test of wild bctr")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

selftests/powerpc: Add a test of wild bctr

This tests that a bctr (Branch to counter and link), ie. a function
call, to a wildly out-of-bounds address is handled correctly.

Some old kernel versions didn't handle it correctly, see eg:

"powerpc/slb: Force a full SLB flush when we insert for a bad EA"
https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-April/157397.html

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>