Fix Drop ALT/CTRL startup issues

[zvecr]

Description

#15953 changed the behaviour of a few core API. With the arm_atsam code implementing its own main logic, this has introduced #16489.

This PR fixes the use of ISSI driver config before init,

• matrix_init called twice - the first time way too early compared to other platforms
• issidrv used before structure configured

Given how the RIOT port has progressed, I didnt see it worth investing a ton of time on the fix.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Fixes [Bug] Drop Alt - QMK configurator generated .bin is bricking the keyboard #16489

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).