hi3516cv6xx: disable CONFIG_IO_STRICT_DEVMEM

[widgetii]

Summary

• The hi3516cv6xx kernel defconfig added in hi3516cv6xx: add Hi3516CV610/Hi3516CV608 family support #2167 enables both `CONFIG_STRICT_DEVMEM=y` and `CONFIG_IO_STRICT_DEVMEM=y`. The latter rejects any `/dev/mem` mmap whose range overlaps a page already claimed by a driver via `request_mem_region()` — even for root.
• That blocks userspace access to every SoC block driven by the kernel: CRG/clocks `0x11010000`, I2C `0x11060000`, SPI `0x11070000`, GPIO `0x11090000+`, UART `0x11040000+`. `ipctool`/`ipcinfo -s` and any similar diagnostic tool fail to read PLLs, probe sensors over I2C/SPI, or dump GPIO state.
• Every other HiSilicon board in the tree that uses `CONFIG_STRICT_DEVMEM=y` already disables `CONFIG_IO_STRICT_DEVMEM` for exactly this reason (hi3516av100, hi3516dv100, hi3516cv500, hi3516av300, hi3516dv300, hi3516ev200, hi3516ev300, hi3516dv200, hi3536dv100, …). This PR aligns hi3516cv6xx with that convention.
• `CONFIG_STRICT_DEVMEM=y` is kept, so /dev/mem still requires CAP_SYS_RAWIO and still gates non-RAM regions. Only the stronger I/O lockout is dropped.

Repro (before)

On OpenIPC `hi3516cv6xx` build, kernel 5.10.221:
```

ipctool

read_mem_reg mmap error: Operation not permitted (1)

ipcinfo -s

read_mem_reg mmap error: Operation not permitted (1)

busybox devmem 0x11010000 32

devmem: mmap: Operation not permitted # CRG/clock0, kernel-claimed
```
Same EPERM behaviour on 0x11040000 (UART), 0x11060000 (I2C), 0x11090000 (GPIO).

Related

• Companion userspace fix: tools: PAGE_SIZE mmap fallback for CONFIG_IO_STRICT_DEVMEM kernels ipctool#172 — falls back from a 64 KiB to a single-page mmap on EPERM, which recovers chip-ID detection even on kernels that keep `IO_STRICT_DEVMEM` enabled.

Test plan

• Diff matches the existing convention used across all V4/V4A HiSi boards in this repo
• Rebuild `br-hi3516cv6xx-musl_defconfig` (or equivalent), flash a CV608 board, confirm `ipctool` emits complete YAML including `clocks:` (PLL frequencies), `sensors:` (I2C probe), and `gpio:`
• Confirm `busybox devmem 0x11010000 32` returns a value instead of EPERM
• `grep STRICT /sys/...` — sanity check that `CONFIG_STRICT_DEVMEM` is still on (still required for non-root attacker hardening)

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