firmware-imx: Install HDMI firmware to standard location
The HDMI firmware is expected to be loaded by firmwared, but it is not
found in the rootfs as shown in systemctl status firmwared:
```
Mar 24 10:25:21 imx8qmmek firmwared[571]: firmware 'hdmitxfw.bin' not found
Mar 24 10:25:21 imx8qmmek firmwared[571]: cancel firmware load hdmitxfw.bin
```
Move the firmware from the sub-folder /lib/firmware/imx/hdmi to the
standard location /lib/firmware.
Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>
