powerpc/watchpoint/ptrace: Return actual num of available watchpoints

User can ask for num of available watchpoints(dbginfo.num_data_bps)
using ptrace(PPC_PTRACE_GETHWDBGINFO). Return actual number of
available watchpoints on the machine rather than hardcoded 1.
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/20200514111741.97993-5-ravi.bangoria@linux.ibm.com

arch/powerpc/kernel/ptrace/ptrace-noadv.c

@@ -44,7 +44,7 @@ void ppc_gethwdinfo(struct ppc_debug_info *dbginfo)
 	dbginfo->version = 1;
 	dbginfo->num_instruction_bps = 0;
 	if (ppc_breakpoint_available())
-		dbginfo->num_data_bps = 1;
+		dbginfo->num_data_bps = nr_wp_slots();
 	else
 		dbginfo->num_data_bps = 0;
 	dbginfo->num_condition_regs = 0;