This updates the USDT argument constraint for powerpc and
powerpc64 from 'nQr' to 'nZr'. The 'Q' memory constraint
will allow a memory operand only if it is an offset from
a register. The 'Z' memory constraint is similar but will
additionally allow a memory operand that is an indexed or
indirect from a register. This offers more flexibility.
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>