hw/arm_sysctl.c: Add the Versatile Express system registers

hw/arm_sysctl.c: Add the Versatile Express system registers

Add support for the Versatile Express SYS_CFG registers, which provide
a generic means of reading or writing configuration information from
various parts of the board. We only implement shutdown and reset.

Also make the RESETCTL register RAZ/WI on Versatile Express rather
than reset the board. Other system registers are generally the same
as Versatile and Realview.

This includes a VMState version number bump for arm_sysctl,
since we have new register state to preserve. It also adds
sys_mci to the VMState while we're bumping the version number
(an accidental omission from commit b50ff6f5).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>