xen/arm: Remove processor specific setup in vcpu_initialise

xen/arm: Remove processor specific setup in vcpu_initialise

This patch introduces the possibility to have specific processor callbacks
that can be called in various place.

Currently VCPU initialisation code contains processor specific setup (for
Cortex A7 and Cortex A15) for the ACTRL registers. It's possible to have
processor with a different layout for this register.

Move this setup in a specific callback for ARM v7 processor.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: marc.ceeeee@gmail.com