hw/intc: Extract the IRQ counting functions into a separate file

hw/intc: Extract the IRQ counting functions into a separate file

These IRQ counting functions will soon be required in binaries that
do not include the APIC code, too, so let's extract them into a
separate file that can be linked independently of the APIC code.

While we're at it, change the apic_* prefix into kvm_* since the
functions are used from the i8259 PIC (i.e. not the APIC), too.

Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20230110095351.611724-2-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>