intc/arm_gic: Add virtualization enabled IRQ helper functions

intc/arm_gic: Add virtualization enabled IRQ helper functions

Add some helper functions to gic_internal.h to get or change the state
of an IRQ. When the current CPU is not a vCPU, the call is forwarded to
the GIC distributor. Otherwise, it acts on the list register matching
the IRQ in the current CPU virtual interface.

gic_clear_active can have a side effect on the distributor, even in the
vCPU case, when the correponding LR has the HW field set.

Use those functions in the CPU interface code path to prepare for the
vCPU interface implementation.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180727095421.386-10-luc.michel@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>