MIPS: lantiq: Remove separate GPHY Firmware loader

The separate GPHY Firmware loader driver is not used any more, the GPHY
firmware is now loaded by the GSWIP switch driver which also makes use
of the GPHY.
Remove the old unused GPHY firmware loader driver.

The GPHY firmware is useless without an Ethernet and switch driver, it
should not harm if loading this does not work for system using an old
device tree.
I am not aware of any vendor separating the device tree from the kernel
binary, it should be ok to remove this.

The code and the functionality form this separate GPHY firmware loader
was added to the gswip driver in commit 14fceff4

 ("net: dsa: Add
Lantiq / Intel DSA driver for vrx200")

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: john@phrozen.org
Cc: netdev@vger.kernel.org