Added multi-pin TDM support.

[ccrome]

This allows you use use more than one TX or RX pin in TDM mode, allowing for up to 64 channels of record or playback data

This fix goes hand-in-hand with the multi-channel USB support. https://github.com/PaulStoffregen/cores/pull/732

input_tdm: every odd channel had every other sample swapped In every odd channel in TDM input (1, 3, 5, 7, 9, 11, 13, 15), every other word was swapped due to an incorrect copy from 32-bits to 16-bits. This fix corrects the odd channels. The Shift-by zeros and the extraneous logical ands are there for clarity, and I verified they don't end up affecting final code optimization as long as optimization is turned on.

[h4yn0nnym0u5e]

This is non-functional, as the changes to TDM output are not complete