Add SK32F077x (SK32F0xx) HAL port, GENERIC_SK32_F077 board and demos

[dadato]

Summary

Add support for the SK32F077xB MCU (SK32F0xx family, ARM Cortex-M0, 128KB
flash / 10KB SRAM) to ChibiOS-Contrib.

This is a self-contained, STM32-independent port: it does not reuse any
shared STM32 LLD and ships its own DMA, RCC and ISR handling, matching the
SK32's register layout.

What is included

• os/hal/ports/SK32/SK32F0xx: full HAL port with native LLDs for
  ADC, EFL (embedded-flash EEPROM emulation), GPT, I2C, PAL, SERIAL, SPI,
  ST, USB, plus the SK32-specific peripherals:
  • KBCU (Keyboard Control Unit): matrix scan + independent LED/RGB
    channels, optional DMA
  • SLED (on-die WS2812-style LED controller): 8/16/32-bit data widths,
    driven over DMA
  • shared DMA (sk32_dma.c) and ISR (sk32_isr.c) support
• os/common/ext/CMSIS/SK32: CMSIS device headers and system init
• os/common/startup/ARMCMx: devices/SK32F0xx, startup_SK32F0xx.mk,
  SK32F077xB.ld (2KB flash pages)
• os/hal/boards/GENERIC_SK32_F077: generic board for the SK32F077xB
• testhal/SK32: ADC, EEPROM, GPIO, IIC, KBCU, SERIAL, SLED, SPI, TIM
  bring-up projects
• demos/SK32: GENERIC_SK32_F077 (+ PROBE / SERIAL variants)

Testing

• All testhal/SK32 and demos/SK32 projects build cleanly with the
  bundled Makefiles.
• The port is validated on real hardware: the SK32F077xB runs QMK firmware
  (keyboard matrix scanning via KBCU, USB HID, VIA dynamic keymaps backed by
  the EFL driver, SLED-driven RGB) and the USB DFU bootloader.

Notes for reviewers

• SK32 flash is erased/written in 2KB pages (not 1KB as on similar
  STM32F0 devices) — the EFL LLD and linker script account for this.
• Only 10KB SRAM; the board/port configuration keeps RAM usage conservative.

Checklist

• Testhal/demo projects build without warnings/errors
• Code follows the ChibiOS-Contrib style (GPL headers, os/hal layout)
• No STM32/shared LLD dependency left in the SK32 port