powerpc/watchpoint: Workaround P10 DD1 issue with VSX-32 byte instructions

POWER10 DD1 has an issue where it generates watchpoint exceptions when
it shouldn't. The conditions where this occur are:

 - octword op
 - ending address of DAWR range is less than starting address of op
 - those addresses need to be in the same or in two consecutive 512B
   blocks
 - 'op address + 64B' generates an address that has a carry into bit
   52 (crosses 2K boundary)

Handle such spurious exception by considering them as extraneous and
emulating/single-steeping instruction without generating an event.

[ravi: Fixed build warning reported by lkp@intel.com]
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201106045650.278987-1-ravi.bangoria@linux.ibm.com