sunxi64: promote mmc 20ms stabilization delay to family-wide

The "mmc: increase stabilization delay 1ms->20ms" patch (Da Xue) fixes
intermittent cold-boot SD/eMMC init failures: the card needs settle time on
first power-up, so a cold power-on fails to read mmc0 while a warm reset works.
It was board-scoped to orangepi3-lts, but it patches generic sunxi_mmc.c
(sunxi_mmc_reset), so every sunxi SoC benefits.

Second board hitting this: orangepi-win (A64) - cold power-on drops to network
boot ("Device 0: unknown device"), a u-boot `reset` then boots fine. Promote
the patch from board_orangepi3-lts/ to the v2026.07-sunxi64 family root so all
A64/H5/H6/H616 boards get the delay. orangepi3-lts keeps it via the family path.

Applies clean on v2026.07-rc4 (sunxi_mmc_reset udelay(1000) -> udelay(20000)).

Signed-off-by: Igor Pecovnik <igor@armbian.com>

Author: igorpecovnik