dm: Implement a CPU uclass

It is useful to be able to keep track of the available CPUs in a multi-CPU
system. This uclass is mostly intended for use with SMP systems.

The uclass provides methods for getting basic information about each CPU.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 941aa0c..1f40887 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -2,6 +2,8 @@
 
 source "drivers/core/Kconfig"
 
+source "drivers/cpu/Kconfig"
+
 source "drivers/demo/Kconfig"
 
 source "drivers/pci/Kconfig"