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>