dt: disable self-tests for !OF_IRQ

Fix OF selftest compile on sparc which does not enable OF_IRQ.

drivers/of/selftest.c:177: undefined reference to `of_irq_parse_one'
drivers/of/selftest.c:197: undefined reference to `of_irq_parse_one'
drivers/of/selftest.c:248: undefined reference to `of_irq_parse_one'
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@linaro.org>

drivers/of/Kconfig

@@ -17,6 +17,7 @@ config PROC_DEVICETREE
 
 config OF_SELFTEST
 	bool "Device Tree Runtime self tests"
+	depends on OF_IRQ
 	help
 	  This option builds in test cases for the device tree infrastructure
 	  that are executed one at boot time, and the results dumped to the