hexagon: include: asm: kgdb: extend DBG_MAX_REG_NUM for "cs0/1"

Need extend maximized number for "cs0/1", the related warning (with
allmodconfig for v4):

  arch/hexagon/kernel/kgdb.c:79: warning: excess elements in array initializer
  arch/hexagon/kernel/kgdb.c:79: warning: (near initialization for 'dbg_reg_def')
  arch/hexagon/kernel/kgdb.c:80: warning: excess elements in array initializer
  arch/hexagon/kernel/kgdb.c:80: warning: (near initialization for 'dbg_reg_def')

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Richard Kuo <rkuo@codeaurora.org>