Move i.MX8 container image loading support to common/spl

To facilitate testing loading i.MX8 container images, move the
parse-container code to common/spl.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 67f0fe8..cde778b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -300,6 +300,7 @@
 F:	arch/arm/include/asm/mach-imx/
 F:	board/freescale/*mx*/
 F:	board/freescale/common/
+F:	common/spl/spl_imx_container.c
 F:	drivers/serial/serial_mxc.c
 F:	include/imx_container.h