dpll: zl3073x: Implement devlink flash callback

dpll: zl3073x: Implement devlink flash callback

Use the introduced functionality to read firmware files and flash their
contents into the device's internal flash memory to implement the devlink
flash update callback.

Sample output on EDS2 development board:
 # devlink -j dev info i2c/1-0070 | jq '.[][]["versions"]["running"]'
 {
   "fw": "6026"
 }
 # devlink dev flash i2c/1-0070 file firmware_fw2.hex
 [utility] Prepare flash mode
 [utility] Downloading image 100%
 [utility] Flash mode enabled
 [firmware1-part1] Downloading image 100%
 [firmware1-part1] Flashing image
 [firmware1-part2] Downloading image 100%
 [firmware1-part2] Flashing image
 [firmware1] Flashing done
 [firmware2] Downloading image 100%
 [firmware2] Flashing image 100%
 [firmware2] Flashing done
 [utility] Leaving flash mode
 Flashing done
 # devlink -j dev info i2c/1-0070 | jq '.[][]["versions"]["running"]'
 {
   "fw": "7006"
 }

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Link: https://patch.msgid.link/20250909091532.11790-6-ivecera@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>