powerpc/ptrace: Add DAWR debug feature info for userspace

This adds new debug feature information so that the DAWR can be
identified by userspace tools like GDB.

Unfortunately the DAWR doesn't sit nicely into the current description
that ptrace provides to userspace via struct ppc_debug_info.  It doesn't
allow for specifying that only some ranges are possible or even the end
alignment constraints (DAWR only allows 512 byte wide ranges which can't
cross a 512 byte boundary).

After talking to Edjunior Machado (GDB ppc developer), it was decided
this was the best approach.  Just mark it as debug feature DAWR and
tools like GDB can internally decide the constraints.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>

Documentation/powerpc/ptrace.txt

@@ -40,6 +40,7 @@ features will have bits indicating whether there is support for:
 #define PPC_DEBUG_FEATURE_INSN_BP_MASK		0x2
 #define PPC_DEBUG_FEATURE_DATA_BP_RANGE		0x4
 #define PPC_DEBUG_FEATURE_DATA_BP_MASK		0x8
+#define PPC_DEBUG_FEATURE_DATA_BP_DAWR		0x10
 
 2. PTRACE_SETHWDEBUG