ARM devboards: Set arm_sysctl properties before init, not after

ARM devboards: Set arm_sysctl properties before init, not after

The ARM devboard models (vexpress-a9, realview, versatilepb, etc)
were accidentally trying to set one of the arm_sysctl properties
after device init. This has now become a fatal error; set the property
before device init where it should be done instead.

Signed-off-by: Peter Maydell <[email protected]>