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/Makefile b/drivers/Makefile
index 5ef58c0..405b64b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -3,6 +3,7 @@
 obj-$(CONFIG_BIOSEMU) += bios_emulator/
 obj-y += block/
 obj-$(CONFIG_BOOTCOUNT_LIMIT) += bootcount/
+obj-$(CONFIG_CPU) += cpu/
 obj-y += crypto/
 obj-$(CONFIG_FPGA) += fpga/
 obj-y += hwmon/