PowerPC remove 512 bytes region limit if 2nd DAWR is avaliable.

Power 10 introduces the 2nd DAWR (second watchpoint) and also removed
a restriction that limit the watch region to 512 bytes.

2020-11-08  Rogerio A. Cardoso  <rcardoso@linux.ibm.com>

/gdb

	* ppc-linux-nat.c: (PPC_DEBUG_FEATURE_DATA_BP_ARCH_31): New define.
	(region_ok_for_hw_watchpoint): Check if 2nd DAWR is avaliable before
	set region.