integrator/cp: Implement CARDIN and WPROT signals

integrator/cp: Implement CARDIN and WPROT signals

This allows to use the SD card emulation of the board: Forward the
signals from the pl181 top the CP control register emulation, report the
current state via CP_INTREG, deliver CARDIN IRQ to the secondary
interrupt controller and also support clearing that line via CP_INTREG.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Message-id: c55d9fb28d19ec83625cb0074b3b6f2e5958caf6.1426004843.git.jan.kiszka@siemens.com
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>