Raspberry PI standby mode

As the Raspberry PI has no proper standby mode from which it can be woken up again, it's so far impossible to turn off the attached display automatically.

This change set allows the PI's video output to be powered down, and back on again (works for HDMI and SDTV). The respective methods of CBRP are exposed as Builtin commands in case someone finds them useful for scripting/testing/working-around-issues.

Also, there's an IPowerSyscall subclass for the PI that simulates Suspend() by powering the display down and back up as required. To trigger the wake up, I had to add some platform specific code to CApplication::OnKey().