[ARM] arm32: Update cpu_proc_v7.S for Cortex-A15

For running Xvisor ARM32 on VExpress-A15 we should be able to
do CPU specific settings in proc_setup() and proc_setup_smp_id()
hence this patch updates this fucntions for cortex-A15.

Signed-off-by: Anup Patel <anup@brainfault.org>