Implement host and two VMs' serial port output and input emulation.

[pengzechen]

I want to start three cores to do that.
core 0 runs vm 0, and core 1 runs vm1
core2 runs a shell that can change serial

[hky1999]

You'd better implement this demo under this branch with axtask.

Still, your design seems strange, ask more dalaos for suggestions. @aarkegz

[pengzechen]

emm, "/tree/task_vcpu" couldn't work now. （can't even do exception handling）
ok

[pengzechen]

@aarkegz Vm managing shell should run in el2 in host?

[hky1999]

of course, if there has to be one.