MLK-21845-3 imx8m: Append HDMI Firmware only for imx8mq

Since only i.MX8MQ needs HDMI firmware packing into boot image. Change
the imximage.cfg with CONFIG_IMX8MQ used.

Signed-off-by: Ye Li <ye.li@nxp.com>

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

@@ -7,7 +7,9 @@
 
 FIT
 BOOT_FROM	sd
+#ifdef CONFIG_IMX8MQ
 SIGNED_HDMI	signed_hdmi_imx8m.bin
+#endif
 LOADER		spl/u-boot-spl-ddr.bin	0x7E1000
 SECOND_LOADER	u-boot.itb		0x40200000 0x60000