The ADIN1300/ADIN1200 support cable diagnostics using TDR.

The cable fault detection is automatically run on all four pairs looking at
all combinations of pair faults by first putting the PHY in standby (clear
the LINK_EN bit, PHY_CTRL_3 register, Address 0x0017) and then enabling the
diagnostic clock (set the DIAG_CLK_EN bit, PHY_CTRL_1 register, Address
0x0012).

Cable diagnostics can then be run (set the CDIAG_RUN bit in the
CDIAG_RUN register, Address 0xBA1B). The results are reported for each pair
in the cable diagnostics results registers, CDIAG_DTLD_RSLTS_0,
CDIAG_DTLD_RSLTS_1, CDIAG_DTLD_RSLTS_2, and CDIAG_DTLD_RSLTS_3, Address
0xBA1D to Address 0xBA20).

The distance to the first fault for each pair is reported in the cable
fault distance registers, CDIAG_FLT_DIST_0, CDIAG_FLT_DIST_1,
CDIAG_FLT_DIST_2, and CDIAG_FLT_DIST_3, Address 0xBA21 to Address 0xBA24).

This change implements support for this using phylib's cable-test support.
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NAlexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201103074436.93790-2-alexandru.ardelean@analog.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>