[CORE] vmm_vcpu_irq: Make VCPU IRQ reason 64-bit

On 64-bit host, we may want to have virtual/physical address as
reason for a VCPU IRQ (e.g. VCPU IRQ for data abort, prefetch
abort, or undefined exception) hence it would lot helpful if
the reason for asserting VCPU IRQ is 64-bit.

The patch makes VCPU IRQ reason 64-bit due to above described rationale.

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