powerpc/watchpoint: Rename current DAWR macros

Power10 is introducing second DAWR. Use real register names from ISA
for current macros:
  s/SPRN_DAWR/SPRN_DAWR0/
  s/SPRN_DAWRX/SPRN_DAWRX0/

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Michael Neuling <mikey@neuling.org>
Link: https://lore.kernel.org/r/20200514111741.97993-2-ravi.bangoria@linux.ibm.com