powerpc/ptrace: Make #defines for all request numbers hex

We have a mix of decimal and hex here, so lets make them consistently
hex.  Also, strace will print them in hex if it can't decode them, so
having them in hex here makes it easier to match up.

No functional change.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>