Fix F411 PA10 Motor DMA Assignment

[ot0tot]

Timer-based DShot does not work on F411 FCs that use pin A10 as a motor output when DMA2 Stream 6 Channel 0 is used for TIM1_CH3. Moving the DMA assignment to DMA2 Stream 6 Channel 6 fixes the issue.

See: betaflight/unified-targets#961

[blckmn]

AUTOMERGE: (FAIL)

• github identifies PR as mergeable -> FAIL
• assigned to a milestone -> PASS
• cooling off period lapsed -> PASS
• commit count less or equal to three -> PASS
• Don't merge label NOT found -> PASS
• at least one RN: label found -> PASS
• Tested label found -> FAIL
• assigned to an approver -> FAIL
• approver count at least three -> FAIL

[github-actions]

Do you want to test this code? Here you have an automated build:
Assets
WARNING: It may be unstable. Use only for testing! See: https://www.youtube.com/watch?v=I1uN9CN30gw for instructions for unified targets!

[ctzsnooze]

Usually we have bitbang set to auto on these FC's.
How does this change affect that setting?
What benefit does this change bring to the affected boards?

[ot0tot]

Usually we have bitbang set to auto on these FC's. How does this change affect that setting? What benefit does this change bring to the affected boards?

I believe DShot bitbang should be set to off on F411 FCs, as due to an errata it is incompatible with DMA on SPI1, which is usually used for the gyro (see:https://betaflight.com/docs/manufacturer/manufacturer-design-guidelines#3213-f4-resource-selection). Regardless, this change does not affect the bitbang settings, it only moves TIM1_CH3 to a different DMA channel in the same stream so that if DShot bitbang is disabled, timer-based DShot works as expected.

Without this change, timer-based DShot does not work on the motor assigned to pin A10, and it also seems to prevent the ADC from working (see troubleshooting discussion linked in the unified-targets PR). Thus a user would not be able to run bidirectional DShot on these FCs, and they would lose ADC functions such as voltage and current monitoring.

It's not clear to me why there is a difference between using channel 0 and channel 6 in this case, but if anyone has an idea I would love to hear it!