[libcpu/arm] remove useless cpsr updating in rt_hw_context_switch_to

This piece of code will enable the interrupt early before switching to
the first thread. Although it is harmless, but not prefect.
[bsp/rva8] enable group{0,1} interrupt forwarding in gic initialization

When RT-Thread is running stand alone, it forgot to enable the
distributor of GIC.
Merge pull request #256 from grissiom/qemu-realview-vmm

Qemu realview vmm