soc: rockchip: grf: Fix SDMMC not working on RK3588 with bus-width > 1

[evtest-hash]

Backports upstream 6f6878ec6faf (v6.6); this tree predates it.

RK3588 SYS_GRF_SOC_CON6 bit 14 (force_jtag) resets to 1 and muxes SDMMC
D2/D3 to JTAG, so bus-width > 1 does not work.

This tree already carries the same "jtag switching" entry for rk3036, rk3128,
rk3228, rk3288, rk3328, rk3368 and rk3399 — RK3588 is simply missing it.

Not a verbatim copy of the upstream hunk: this tree's
rk3588_sys_grf_defaults already carries a vendor-specific
"Connect EDP hpd to IO" entry, so the patch adds one line to the existing
array instead of introducing mainline's version of it.

Tested on Mixtile Core 3588E (Ubuntu 24.04, kernel 6.1.172-rockchip-vendor):
boots normally, SYS_GRF_SOC_CON6 reads 0x000007c7 (bit 14 = 0).

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Walkthrough

The change defines RK3588_SYS_GRF_SOC_CON6 at offset 0x0318. It adds a "jtag switching" entry to rk3588_sys_grf_defaults. The entry writes HIWORD_UPDATE(0, 1, 14) to the new register.

Priority: ➖ Normal

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 3fa8f

The change correctly applies the RK3588 JTAG-switching default, with no unresolved merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the RK3588 GRF change and its purpose: fixing SDMMC operation for bus widths greater than 1.
Description check	✅ Passed	The description directly explains the RK3588 JTAG mux issue, the backported fix, the preserved vendor-specific entry, and the test result.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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