mediatek: filogic: fix Globitel BT-R320 FIT rootfs mapping

mediatek: filogic: fix Globitel BT-R320 FIT rootfs mapping

Globitel BT-R320 boots the sysupgrade FIT from the eMMC production
partition with root=/dev/fit0.

The device tree did not describe the production GPT partition and
/chosen/rootdisk did not point at the FIT container. fitblk then had no
rootdisk match and the board stopped at:

  Waiting for root device /dev/fit0...

Describe the eMMC GPT partitions, set /chosen/rootdisk to production,
and use the FIT sysupgrade path.

Fixes: a3105d3f9573 ("mediatek: filogic: add support for Globitel BT-R320")
Signed-off-by: solodecode <zikwarface134@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23895
Signed-off-by: Robert Marko <robert.marko@sartura.hr>