Allow for WS2812 PWM to work on DMAMUX-capable devices

[tzarc]

Description

Newer STM32 MCUs have a DMAMUX peripheral, which allows mapping of DMAs to different DMA streams, rather than hard-defining the target streams in silicon.

Affects STM32L4+ devices, as well as the soon-to-be-supported-by-QMK STM32G4/H7 families.

Tested on F303/Proton-C (ChibiOS v19, non-DMAMUX), G474 (ChibiOS v20, with DMAMUX).

Types of Changes

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

Checklist

• My code follows the code style of this project.
• 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).

[zvecr]

Wont the removal of WS2812_DMA_STREAM stop configuration of TIM1_UP on stm32f4 (dma2, steam 5, channel 6)?

[tzarc]

Wont the removal of WS2812_DMA_STREAM stop configuration of TIM1_UP on stm32f4 (dma2, steam 5, channel 6)?

Internally, ChibiOS would make it index 14, i.e. you'd need #define WS2812_DMA_CHANNEL 14.
The fun part here is that it's 0-indexed, but for the F3 it's 1-indexed.
As for channel 6 -- in the stm32_registry.h it defines:

#define STM32_DMA2_CH6_NUMBER               69

....which really only maps to the interrupt vector.

Either way, it's clear as mud... so I'm inclined to rollback that portion of this PR.

[drashna]

__attribute__((weak)) ✅