[MYON2][BOARD] Rework application of revision-dependent overlays

During SW validation I noticed that the older way of applying revision-specific overlays was broken. Rather than fixing that, I thought it would be a good time to implement a proper way of doing this with seco_fdt_oerlay. MR: [CMD][FDT_OVERLAY] Add support for custom overlays (!232)

Currently for audio codecs based on board revision.