drivers: video: ov5640: Use CCI API helpers for register access

Replace the custom I2C read/write functions in the OV5640 driver
with the common Video CCI API helpers.

- Introduce OV5640_REG8/REG16 macros for register addressing
- Convert struct ov5640_reg to struct video_reg16
- Replace ov5640_{read,write,modify}_reg() with CCI API helpers
- Replace ov5640_write_multi_regs() with video_write_cci_multiregs16()

This aligns the OV5640 driver with other video sensor drivers
that already rely on the CCI helpers.

Signed-off-by: Khanh Nguyen <[email protected]>

Author: KhanhNguyen-RVC