soc/intel: Introduce ioapic_get_sci_pin()

According to ACPI Release 6.5 systems supporting PIC (i8259)
interrupt mechanism need to report IRQ vector for the SCI_INT
field. In PIC mode only IRQ0..15 are allowed hardware vectors.

This change should cover section 5.2.9 to not pass SCI_INT
larger than IRQ15. Section 5.2.15.5 needs follow-up work.

Care should be taken that ioapic_get_sci_pin() is called
after platform code has potentially changed the routing
from the default.

It appears touched all platforms except siemens/mc_aplX
currently program SCI as IRQ9.

Change-Id: I723c207f1dcbba5e6fc0452fe1dbd087fad290ee
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74326
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <inforichland@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/arch/x86/include/arch/ioapic.h

@@ -22,6 +22,8 @@ void register_new_ioapic(void *ioapic_base);
 void register_new_ioapic_gsi0(void *ioapic_base);
 
 void ioapic_set_boot_config(void *ioapic_base, bool irq_on_fsb);
+
+void ioapic_get_sci_pin(u8 *gsi, u8 *irq, u8 *flags);
 #endif
 
 #endif