cmd: Add Kconfig option for multiprocessor cmds

Add Kconfig option(CONFIG_CMD_MP) to enable or disable multiprocessor
commands. Compile cmd/mp.c based on CONFIG_CMD_MP.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/cmd/Makefile b/cmd/Makefile
index fb133e3..166c652 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -100,7 +100,7 @@
 obj-$(CONFIG_CMD_SLEEP) += sleep.o
 obj-$(CONFIG_CMD_MMC) += mmc.o
 obj-$(CONFIG_CMD_OPTEE_RPMB) += optee_rpmb.o
-obj-$(CONFIG_MP) += mp.o
+obj-$(CONFIG_CMD_MP) += mp.o
 obj-$(CONFIG_CMD_MTD) += mtd.o
 obj-$(CONFIG_CMD_MTDPARTS) += mtdparts.o
 obj-$(CONFIG_CMD_CLONE) += clone.o