hw/arm/iotkit-sysctl: Implement CPUWAIT and INITSVTOR*

hw/arm/iotkit-sysctl: Implement CPUWAIT and INITSVTOR*

The CPUWAIT register acts as a sort of power-control: if a bit
in it is 1 then the CPU will have been forced into waiting
when the system was reset (which in QEMU we model as the
CPU starting powered off). Writing a 0 to the register will
allow the CPU to boot (for QEMU, we model this as powering
it on). Note that writing 0 to the register does not power
off a CPU.

For this to work correctly we need to also honour the
INITSVTOR* registers, which let the guest control where the
CPU will load its SP and PC from when it comes out of reset.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190219125808.25174-8-peter.maydell@linaro.org