[IMX8MM][MYON2] Add support of Myon II i.MX8M Mini module

Add support of Myon II i.MX8M Mini module with ConXM carrier.

This MR contains changes ported from SECO NE Linux: seco-ne/kernel/linux-imx-kuk!442 (merged) and seco-ne/kernel/linux-imx-kuk!561 (merged). In particular:

• ported seconorth-myon2-conxm-hdmi and seconorth-myon2-conxm-atm0700l61ct device trees;
• added SECO version of rohm-bd718x7 driver with optional interrupts.

Other changes introduced in the MR:

• Added support of audio (for V1R4 board with wm8983 audio codec):
  • Imported changes for audio codec from kuk kernel;
  • Cherry-picked commit from NXP kernel for imx-sdma to fix kernel crash when starting audio playback.
• Added missing SPI2 node in dts and fixed pinmuxing for it. Removed unused UART4.