Added comments : gic, virq, virqmap, Refactor : GIC feature, VIRQ map macro, guest context init

Refactor
gic.c, remove function name "test"
1. gic_test_configure_irq -> gic_configure_irq
2. gic_test_set_irq_handler -> gic_set_irq_handler
3. remove unused parameter of gic_set_irq_handler, *pdata 

VIRQ map macro
1. Remove CFG_GUEST1_VIRQMAP because It was used.
2. CFG_GUEST0_VIRQMAP -> CFG_GUEST_VIRQMAP 

Guest context init
There is duplicated code, so puts it for loop.