Add a 'cpu' command to print CPU information

Add a simple command which provides access to a list of available CPUs along
with descriptions and basic information.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/common/Makefile b/common/Makefile
index fba3830..9084c73 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -74,6 +74,7 @@
 obj-$(CONFIG_CMD_CLK) += cmd_clk.o
 obj-$(CONFIG_CMD_CONSOLE) += cmd_console.o
 obj-$(CONFIG_CMD_CPLBINFO) += cmd_cplbinfo.o
+obj-$(CONFIG_CMD_CPU) += cmd_cpu.o
 obj-$(CONFIG_DATAFLASH_MMC_SELECT) += cmd_dataflash_mmc_mux.o
 obj-$(CONFIG_CMD_DATE) += cmd_date.o
 obj-$(CONFIG_CMD_DEMO) += cmd_demo.o