The StrongARM GPIO GPSR and GPCR registers are write-only, with reads being
undefined behaviour. Instead of having GPCR return 31337 and GPSR return
the value last written, make both log the guest error and return 0.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>