[][kernel][mt7988][eth][i2.5Gphy: Add safer sequence to loadfirmware]

[Description]
Add safer sequence to loadfirmware and other changes:

1. We need a safer firmware load sequence:
- power off the whole i2.5Gphy
- power on the whole i2.5Gphy
- Load PMb
- set fw trigger bit
2. Remove DMb firwmare loading flow. We don't need to load it anymore.
3. Change firwmare location to fit upstream style.
4. Fix 16-bit next page exchange issue.
5. Load firmware only once after booting up. So if user trigger
"ifconfig <interface> up/down", we won't load firmware again.

Without this patch, internal 2.5Gphy can't work correctly if you use
i2.5Gphy versino Uboot.

[Release-log]
N/A

Change-Id: I545e25424cba0cf7ccf16cc06fc6452703cf879a
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8244059
15 files changed