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

Added comments : gic.*, virq.*, virqmap.*

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. Removes CFG_GUEST1_VIRQMAP, because It didn't be used to map.
2. CFG_GUEST0_VIRQMAP -> CFG_GUEST_VIRQMAP

Guest context init
There is duplicated code, so puts it for loop.

Fixed styling 
config/cfg_platform.h : Its styling has not been checked.