SN32 boards cleanup

[dexter93]

There is no reason for shared key/led matrix keyboards to nerf plain keyboard setups.
Make a new board for them that preselects PWM and disables SWD/RESET pins since they're usually allocated as part of the matrix

usage: in keyboard.json/info.json

    "development_board": "sn32f240b_shared_matrix"

instead of the old

    "processor": "SN32F248BF",
    "bootloader": "sn32-dfu",

since those are preselected now

Description

Requires ChibiOS/ChibiOS-Contrib#411

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

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).

[github-actions]

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