imx: add rom api support

i.MX8MN support loading images with rom api, so we implement
reuse board_return_to_bootrom to let ROM loading images.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/Makefile b/arch/arm/mach-imx/Makefile
index 6e87dc5..e14713c 100644
--- a/arch/arm/mach-imx/Makefile
+++ b/arch/arm/mach-imx/Makefile
@@ -226,3 +226,5 @@
 obj-$(CONFIG_ARCH_MX7ULP) += mx7ulp/
 obj-$(CONFIG_IMX8M) += imx8m/
 obj-$(CONFIG_ARCH_IMX8) += imx8/
+
+obj-$(CONFIG_SPL_BOOTROM_SUPPORT) += spl_imx_romapi.o