Guest Address Space Changed: 1GB->4GB & SPSR_irq saved in guest contexts

- Stage 2 IPA:PA mapping for Guest Address Space Changed
- context.c: saves spsr_irq, sp_irq, lr_irq in a guest context to safely preempt guest running in IRQ mode

Guest Address Space: 1GB -> 4GB
- 0x0000_0000 ~ 1GB Peripherals
- 0x4000_0000 ~ 1GB Unmapped
- 0x8000_0000 ~ 1GB RAM, code entry, 256MB ~ 1GB mapped memory
- 0xC000_0000 ~ 1GB Unmapped
- Guest 0: 768MB RAM
- Guest 1: 256MB RAM
- Guest Code Entry Changed: 0x0000_0000 -> 0x8000_0000