dac_output, LED_BUILTIN and override pins

[pschatzmann]

• Provide LED_BUILTIN for LED
• Allow to override pins in generic board_def.h when using PlatformIO
• proper support to be able to select earphones or amplifier in dac_output

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This discussion was created from the release dac_output, LED_BUILTIN and override pins .

[kaushleshchandel]

Very useful. Thanks