sandbox: Add a test for IRQ

Add a simple sandbox test for this uclass.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index 04c4951..2a9161c 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -100,6 +100,7 @@
 CONFIG_CROS_EC_LPC=y
 CONFIG_CROS_EC_SANDBOX=y
 CONFIG_CROS_EC_SPI=y
+CONFIG_IRQ=y
 CONFIG_PWRSEQ=y
 CONFIG_SPL_PWRSEQ=y
 CONFIG_I2C_EEPROM=y