[nto] Fix nto target stopped by watchpoint.

[nto] Fix nto target stopped by watchpoint.

Fix 'stopped by watchpoint' detection: add inferior data, use inferior data
for storing last stopped flags needed for detection.

gdb/ChangeLog:

	* nto-procfs.c (procfs_wait): Set stopped_flags nad stopped_pc.
	(procfs_stopped_by_watchpoint): Use flags stored in inferior data.
	* nto-tdep.c (nto_new_inferior_data_reg): New definition.
	(nto_new_inferior_data, nto_inferior_data_cleanup, nto_inferior_data):
	New functions.
	(_initialize_nto_tdep): New forward declaration, new function.
	* nto-tdep.h (struct nto_inferior_data): New struct.
	(nto_inferior_data): New function declaration.