This commit reorganizes SPI flash header files to better reflect their
visibility and intended usage:
1. Rename `esp_flash_port/` to `esp_flash_chips/`:
- Better reflects that these headers are for chip driver implementations
- All chip driver headers moved to `esp_flash_chips/` directory
- Added README.md explaining semi-public nature of these headers
2. Move internal headers to `esp_private/`:
- `esp_flash_internal.h` -> `esp_private/esp_flash_internal.h`
- `memspi_host_driver.h` -> `esp_private/memspi_host_driver.h`
3. Move chip driver related headers to `esp_flash_chips/`:
- `esp_private/esp_flash_types.h` -> `esp_flash_chips/esp_flash_types.h`
- `spi_flash/spi_flash_defs.h` -> `esp_flash_chips/spi_flash_defs.h`
- `spi_flash_override.h` -> `esp_flash_chips/spi_flash_override.h`
- All `spi_flash_chip_*.h` headers moved to `esp_flash_chips/`
4. Code improvements:
- Remove unused includes (e.g., `spi_flash_override.h` from `cache_utils.c`)
- Use public API `esp_flash_get_size()` instead of direct member access
- Add `esp_flash_is_quad_mode` to linker.lf for IRAM placement
5. Documentation updates:
- Add README.md in `esp_flash_chips/` explaining semi-public headers
- Update programming guide with warnings about internal headers
- Update both English and Chinese documentation
6. Update all references across the codebase:
- Update includes in `spi_flash` component
- Update `bootloader_support`, `app_update`, `esp_tee`, `espcoredump`
- Update example projects
Breaking changes:
- Headers moved to new locations require include path updates
- `custom_flash_driver` example temporarily disabled until external
components are updated
