AP_Bootloader: reserve ID 1302 for CBU_H753-SOM

[julianoes]

Reserve the board ID for the CBUnmanned H753-SOM so the upcoming PX4 board bringup does not cause conflicts later.

See: https://www.cbunmanned.com/

Summary

Classification & Testing (check all that apply and add your own)

• Checked by a human programmer
• Non-functional change
• No-binary change
• Infrastructure change (e.g. unit tests, helper scripts)
• Automated test(s) verify changes (e.g. unit test, autotest)
• Tested manually, description below (e.g. SITL)
• Tested on hardware
• Logs attached
• Logs available on request

Description

[julianoes]

Thanks @andyp1per!