Compatibility layer update2

Created by: lorforlinux

@jadonk @RobertCNelson please review my code :)

This update includes these major changes,

1. Removed *gpio_input_pin pinmux nodes for BBB and BBAI.
2. Added remaining PRU pinmux nodes (eCAP and UART).
3. Created bone_emmc label and compatible DT overlay.
4. New gpio_* macros for each Header pins.
5. Updated BBAI bone-pinmux-helper nodes.
6. Updated comments to point this repo (v4.19.x.ti-overlays).
7. Replace CTAG SW 16ch (for v4.4) with CTAG SW 8ch for (v4.14 and above).
8. Updated DT overlay names e.x. ECAP -> eCAP.