bl5340_dvk_cpuapp has wrong button for mcuboot button

[nordicjm]

Describe the bug
The bl5340 dvk board has a dedicated boot button, instead the mcuboot button is using one of the 4 application buttons, which is wrong, and pulls in the whole i2c driver and port expander driver, which conversely makes mcuboot far too big to build for the board.

Environment (please complete the following information):

• Commit SHA or Version used: 4d906d9

[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.

[kartben]

Closing with the correct reason as this was improperly marked as "completed".