powerpc, hw_breakpoint: Tell generic code we have no instruction breakpoints

At present, hw_breakpoint_slots() returns 1 regardless of what
type of breakpoint is specified in the type argument.  Since we
don't define CONFIG_HAVE_MIXED_BREAKPOINTS_REGS, there are
separate values for TYPE_INST and TYPE_DATA, and hw_breakpoint_slots()
returns 1 for both, effectively advertising instruction breakpoint
support which doesn't exist.

This fixes it by making hw_breakpoint_slots return 1 for TYPE_DATA
and 0 for TYPE_INST.  This moves hw_breakpoint_slots() from the
powerpc hw_breakpoint.h to hw_breakpoint.c because the definitions
of TYPE_INST and TYPE_DATA aren't available in <asm/hw_breakpoint.h>.
They are defined in <linux/hw_breakpoint.h> but we can't include
that header in <asm/hw_breakpoint.h>, and nor can we rely on
<linux/hw_breakpoint.h> being included before <asm/hw_breakpoint.h>.
Since hw_breakpoint_slots() is only called at boot time, there is
no performance impact from making it a real function rather than
a static inline.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/hw_breakpoint.c

@@ -43,6 +43,16 @@
  */
 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
 
+/*
+ * Returns total number of data or instruction breakpoints available.
+ */
+int hw_breakpoint_slots(int type)
+{
+	if (type == TYPE_DATA)
+		return HBP_NUM;
+	return 0;		/* no instruction breakpoints available */
+}
+
 /*
  * Install a perf counter breakpoint.
  *