Update satisfaction75 to only use keyboard datablock

[zvecr]

Description

Preparing for changes where via.h is not always on the path, and the feature is handed over, this PR:

• Removes unconditional use of via.h
• Migrates use of VIA_EEPROM_CUSTOM_CONFIG_SIZE to always use keyboard datablock
• Updates eeprom init in line with recent changes to develop

Types of Changes

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

Issues Fixed or Closed by This PR

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).