[][openwrt][mt7988][app][Add utility for configuring Mxl series ethernet switchs]

[Description]
Add the 'ethswbox' utility for configuring Mxl series ethernet switchs.
The commands currently supported and successfully verified are as follows:
(1). ./fapi-int-gphy-read phy=0x0 mmd=0x0 reg=0x2
(2). ./fapi-int-gphy-write phy=0x0 mmd=0x7 reg=0x3c data=0x2
(3). ./ssb_smdio_download mxl86282c_1122_1137_1136_0035_signed_dsa_smdio_xfi.bin

[Release-log]
N/A


Change-Id: I6d9d49b4384dbee0343e06270356c7bd942744b3
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/9033056
61 files changed