arm/vm_event: get/set registers

arm/vm_event: get/set registers

Add support for getting/setting registers through vm_event on ARM. Only
TTB/CR/R0/R1, PC and CPSR are sent as part of a request and only PC is set
as part of a response. The set of registers can be expanded in the future to
include other registers as well if necessary.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>