target-arm/cpu64.c: Actually register Cortex-A57 impdef registers

target-arm/cpu64.c: Actually register Cortex-A57 impdef registers

cpu64.c contains a reginfo list for the impdef registers on
the Cortex-A57; however we forgot to actually call define_arm_cp_regs(),
so it was sitting there doing nothing. Remedy this omission.

Message-id: 1401226259-23121-1-git-send-email-peter.maydell@linaro.org
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Tested-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>