util/sconfig: Remove unused ioapic and irq keywords

Ioapic information in the devicetree was only used to set up mptables
but this generic driver was removed (ca5a793 drivers/generic/ioapic:
Drop poor implementation).

This removes the unused remainders from mainboard devicetrees.
Remove ioapic setup from sconfig.

Change-Id: Ib3fef0bf923ab3f02f3aeed2e55cf662a3dc3a1b
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71789
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

src/mainboard/lenovo/t400/variants/t400/overridetree.cb

@@ -25,7 +25,6 @@ chip northbridge/intel/gm45
 			end
 			device pci 1f.3 on # SMBus
 				subsystemid 0x17aa 0x20f9
-				ioapic_irq 2 INTC 0x12
 				# eeprom, 8 virtual devices, same chip
 				chip drivers/i2c/at24rf08c
 					device i2c 54 on end