cris: arch-v10: kgdb: Use BAR instead of DTP0 for register P12

For arch-v10, there is no DTP0 register, and at present, assembler know
BAR, so use BAR instead of DTP0, the related error (with allmodconfig):

    CC      arch/cris/arch-v10/kernel/kgdb.o
  {standard input}: Assembler messages:
  {standard input}:6: Error: Illegal operands
  {standard input}:6: Error: Illegal operands

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Acked-by: Hans-Peter Nilsson <hp@axis.com>
Signed-off-by: Jesper Nilsson <jespern@axis.com>