x86: Move UCLASS_IRQ into a separate file

Update this uclass to support the needs of the Apollo Lake ITSS. It
supports four operations.

Move the uclass into a separate directory so that sandbox can use it too.
Add a new Kconfig to control it and enable this on x86.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/Kconfig b/arch/Kconfig
index e1f1fcd..6865e1f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -186,6 +186,7 @@
 	imply USB_HOST_ETHER
 	imply PCH
 	imply RTC_MC146818
+	imply IRQ
 
 	# Thing to enable for when SPL/TPL are enabled: SPL
 	imply SPL_DM