Revert "imx8mn: Add target for iMX8MN eMMC partition boot support"

This reverts commit 952f6cf50493beb03d5d4a80d26f9661d61d801a.

Since SPL rom_api driver can check the boot device and image offset from
ROM, we can adjust FIT load address for eMMC boot, so no need such
target for emmc including normal boot and fastboot.

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/iMX8M/soc.mak b/iMX8M/soc.mak
index 990d063..a6ba3bd 100644
--- a/iMX8M/soc.mak
+++ b/iMX8M/soc.mak
@@ -179,9 +179,6 @@
 	./mkimage_imx8 -version $(VERSION) -dev flexspi -fit -loader u-boot-spl-ddr4.bin $(SPL_FSPI_LOAD_ADDR) -second_loader u-boot-ddr4-evk.itb 0x40200000 0x60000 -out $(OUTIMG)
 	./$(QSPI_PACKER) $(QSPI_HEADER)
 
-flash_ddr4_evk_emmc_fastboot: $(MKIMG) u-boot-spl-ddr4.bin u-boot-ddr4-evk.itb
-	./mkimage_imx8 -version $(VERSION) -dev emmc_fastboot -fit -loader u-boot-spl-ddr4.bin $(SPL_LOAD_ADDR) -second_loader u-boot-ddr4-evk.itb 0x40200000 0x60000 -out $(OUTIMG)
-
 flash_hdmi_spl_uboot: flash_evk
 
 flash_dp_spl_uboot: flash_dp_evk