Merge pull request #142 from in1004kyu/v1

Added comments : gic, virq, virqmap, Refactor : GIC feature, VIRQ map macro, guest context init
virtual device : Removed ARM architecture dependencies in virtual device.
Merge pull request #166 from joohyun0115/vdev_framework

Removed ARM architecture dependencies in virtual device.
[GUEST] Move receiving vtimer interrupt code to c_start.c

This patch separates virtual timer from gic