hw/rtc/mc146818rtc: Make the mc146818 RTC device target independent

hw/rtc/mc146818rtc: Make the mc146818 RTC device target independent

The only reason for this code being target dependent was the IRQ-counting
related code in rtc_policy_slew_deliver_irq(). Since these functions have
been moved into a new, separate file (kvm_irqcount.c) which is now always
compiled and linked if necessary, we can get rid of the #ifdef TARGET_I386
switches in mc146818rtc.c and declare it in the softmmu_ss instead of
specific_ss, so that the code only gets compiled once for all targets.

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: <20230110095351.611724-4-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>