add in-game brightness hotkeys L3 + L1 and L3 + R1 for RG351P

[amd343]

Pull Request Template

Description

add in-game brightness hotkeys L3 + L1 and L3 + R1 for RG351P

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] This change requires a documentation update

How Has This Been Tested Locally?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

tested on RG351P while in retroarch. only works in-game and not globally

Test Configuration:

• Build OS name and version: Ubuntu 20.04 LTS
• Docker (Y/N): N
• JELOS Branch: stable
• Any additional information that may be useful: uses if HW_DEVICE is RG351P then appends to 98-jslisten

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation: I can't figure out how to edit the wiki --> Global Hotkeys to add documentation for the shortcut.

Note: This PR template is adapted from embeddedartistry