Implement dmsai core device driver through dmdevfs

[JaxCalder]

Summary

• Implement the architecture-independent dmsai dmdrvi DIF: parse the dmdevfs-selected INI section, reserve one SAI port, expose /dev/dmsaiN, manage an exclusive open handle, and forward whole-frame PCM read/write to the port.
• Implement START/STOP, configuration/status and per-handle timeout ioctls, stat, and flush. Add DMSAI_IOCTL_DRAIN so applications using Dmod_FileOpen can wait until TX has actually reached the output before STOP. The STM32 DMA engine tracks completed halves for this wait.
• Accept padded TDM frames in the existing STM32 port, matching the F769 board config. Bump both modules to 0.2 because the core now requires the new port drain entry point.
• Update API docs, README and examples. Preserve the existing tests, Makefile, CI and license badges.

Validation

• Built dmsai, dmsai_port, dmsai_driver_board_test, dmsai_port_board_test and existing test_dmsai for STM32F7.
• Installed local .dmf and .dmfc for the core, port and new test, plus the STM32F746G-DISCO SAI2 board config, into dmod-boot. Removed modules.dmp, its object and the config filesystem image before rebuilding. OpenOCD flashed and verified the firmware.
• After 30 seconds, UART responded and ls /dev showed /dev/dmsai1. Ran dmsai_driver_board_test twice through the shell: both runs reported PASS (0).
• The board test checks config/status, per-handle timeout, invalid and unknown ioctl errors, exclusive open, repeated START/STOP, a 300-frame DMA write, TX drain, RX read, drain-after-stop error and reopen. The dmdevfs error log during the second-open probe is expected.

The board test verifies digital DMA transfer and device control. WM8994 analog playback/capture is outside this test because codec setup belongs to its own driver.