Add DDR4 and DDR3L build targets:
flash_ddr4_arm2 and flash_ddr3l_arm2 with HDMI FW contained
flash_ddr4_arm2_no_hdmi and flash_ddr3l_arm2_no_hdmi without HDMI FW.

Rename flash_hdmi_spl_uboot and flash_spl_uboot to
flash_evk and flash_evk_no_hdmi. But still keep the old targets for compatible.

U-boot files for DDR3L or DDR4 build:
  Copy u-boot/u-boot-nodtb.bin to iMX8M/
  Copy u-boot/spl/u-boot-spl.bin to iMX8M/
  Copy u-boot/arch/arm/dts/fsl-imx8mq-ddr3l-arm2.dtb or fsl-imx8mq-ddr4-arm2.dtb
  to iMX8M/
  Copy u-boot/tools/mkimage to iMX8M/mkimage_uboot

DDR FW for DDR3L or DDR4:
  Copy ddr3_dmem_1d.bin and ddr3_imem_1d.bin from linux-imx-firmware
  Copy ddr4_dmem_1d.bin, ddr4_imem_1d.bin, ddr4_dmem_2d.bin and ddr4_imem_2d.bin
  from linux-imx-firmware

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 4f375525)