mx6: add support of multi-processor command

This allows u-boot to load different OS or Bare Metal application on
different cores of the i.MX6 SoC.
For example: running Android on cpu0 and a RT OS like QNX/FreeRTOS on cpu1.

Signed-off-by: Gabriel Huau <contact@huau-gabriel.fr>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/cpu/armv7/mx6/Makefile b/arch/arm/cpu/armv7/mx6/Makefile
index 6dc9f8e..bf6effc 100644
--- a/arch/arm/cpu/armv7/mx6/Makefile
+++ b/arch/arm/cpu/armv7/mx6/Makefile
@@ -10,3 +10,4 @@
 obj-y	:= soc.o clock.o
 obj-$(CONFIG_SPL_BUILD)	     += ddr.o
 obj-$(CONFIG_SECURE_BOOT)    += hab.o
+obj-$(CONFIG_MP)             += mp.o