Remove IRQ_SLOT_COUNT on all boards without PIRQ table.

This config is used only to generate PIRQ table. If no such table is
supplied there is no need for config.

Change-Id: I537d440f53019a6bf7f190446074e75e7420545a
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/7566
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)

src/mainboard/intel/baskingridge/Kconfig

@@ -26,10 +26,6 @@ config MMCONF_BASE_ADDRESS
 	hex
 	default 0xf0000000
 
-config IRQ_SLOT_COUNT
-	int
-	default 18
-
 config MAX_CPUS
 	int
 	default 16