arm64: dts: renesas: gray-hawk: Specify ethernet PHY reset timings

The KSZ9031RNX reference manual [1] DS00002117K page 62 FIGURE 7-5:
POWER-UP/POWER-DOWN/RESET TIMING Note 2 states, that after the
de-assertion of reset, wait a minimum of 100 us before starting
programming on the MIIM (MDC/MDIO) interface. Set DT property
reset-deassert-us to three times that, 300 us, to provide ample
time between reset deassertion and MDIO access.

The KSZ9031RNX reference manual [1] DS00002117K page 62 TABLE 7-4:
POWER-UP/POWER-DOWN/RESET TIMING PARAMETERS row tSR Stable supply
voltages to de-assertion of reset is at minimum 10 ms. Set DT
property reset-assert-us to 10ms because the KSZ9031RNX RM does
not explicitly spell out how long the reset has to be asserted,
but this at least covers the worst case scenario.

[1] https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/DataSheets/KSZ9031RNX-Data-Sheet-DS00002117.pdf

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260505034325.167797-12-marek.vasut+renesas@mailbox.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

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