imx: imx8m: introduce imximage cfg file

imximage.cfg will be used to generate the flash.bin
Signed-off-by: NPeng Fan <peng.fan@nxp.com>

arch/arm/mach-imx/imx8m/imximage.cfg

+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2018 NXP
+ */
+
+#define __ASSEMBLY__
+
+FIT
+BOOT_FROM	sd
+SIGNED_HDMI	signed_hdmi_imx8m.bin
+LOADER		spl/u-boot-spl-ddr.bin	0x7E1000
+SECOND_LOADER	u-boot.itb		0x40200000 0x60000
+
+DDR_FW lpddr4_pmu_train_1d_imem.bin
+DDR_FW lpddr4_pmu_train_1d_dmem.bin
+DDR_FW lpddr4_pmu_train_2d_imem.bin
+DDR_FW lpddr4_pmu_train_2d_dmem.bin