Add SK32F077xB (SK32F0xx) HAL port with GENERIC_SK32_F077 board, testhal and demos

[dadato]

Summary

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

The port is fully native: it does not reuse any shared STM32 low level
driver. Although register-compatible with the STM32F072 for most of the core
(except the USB IP), the SK32 units use the legacy SR/DR register set for
USART/SPI/I2C and carry 3Think-specific peripherals (KBCU, SLED), so every
driver ships its own RCC/clock, DMA and NVIC handling tuned to the vendor
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-only peripherals:
  • KBCU (Keyboard Control Unit): keyboard matrix scan (independent
    mode) and RGB LED column output over DMA1 ch4
  • SLED (on-die WS2812-style serial LED controller): two groups,
    8/16/32-bit data widths, DMA-driven
  • shared native DMA helper sk32_dma.c and ISR aggregation sk32_isr.c
• os/common/ext/CMSIS/SK32: vendor CMSIS device headers + system init
• os/common/startup/ARMCMx: devices/SK32F0xx, startup_SK32F0xx.mk,
  SK32F077xB.ld (2KB flash pages)
• os/hal/boards/GENERIC_SK32_F077: generic board with the SK32 pin/clock
  definitions
• testhal/SK32: ADC, EEPROM, GPIO, IIC, KBCU, SERIAL, SLED, SPI, TIM
  bring-up projects (all STM32-independent, SK32_* mcuconf naming only)
• demos/SK32: GENERIC_SK32_F077 LED blinker demo

Testing

• Every testhal/SK32 project and the demo build cleanly with their bundled
  Makefiles (arm-none-eabi-gcc, no warnings).
• Validated on real SK32F077xB silicon through QMK firmware: KBCU matrix
  scanning, USB HID + DFU, VIA dynamic keymaps persisted via the EFL driver,
  and SLED-driven RGB output all run on this port.

Notes

• SK32 flash is erased/written in 2KB pages (unlike the 1KB pages of the
  register-compatible STM32F072); the EFL LLD and linker script account for
  this.
• Only 10KB SRAM is available; the port and demos keep RAM usage
  conservative.

Checklist

• All testhal/demos compile cleanly (no warnings/errors)
• No dependency on shared STM32 LLDs or STM32 mcuconf naming remains
• Code layout follows ChibiOS-Contrib conventions