Reduce need for UNUSED

Marlin/src/HAL/HAL_AVR/HAL.h

Marlin/src/HAL/HAL_AVR/HAL_SPI.cpp

Marlin/src/HAL/HAL_DUE/HAL_SPI.cpp

Marlin/src/HAL/HAL_DUE/MarlinSerialUSB.cpp

Marlin/src/HAL/HAL_DUE/usb/sd_mmc_spi_mem.cpp

Marlin/src/HAL/HAL_ESP32/watchdog.h

Marlin/src/HAL/HAL_LINUX/HAL.h

Marlin/src/HAL/HAL_LINUX/include/serial.h

Marlin/src/HAL/HAL_LPC1768/MarlinSerial.h

Marlin/src/HAL/HAL_STM32/HAL.cpp

Marlin/src/HAL/HAL_STM32_F4_F7/HAL.h

Marlin/src/HAL/HAL_TEENSY31_32/HAL.h

Marlin/src/HAL/HAL_TEENSY35_36/HAL.h

Marlin/src/HAL/shared/Delay.h

Marlin/src/feature/Max7219_Debug_LEDs.h

Marlin/src/feature/leds/pca9632.cpp

Marlin/src/feature/power_loss_recovery.h

Marlin/src/feature/runout.h

Marlin/src/feature/spindle_laser.h

Marlin/src/gcode/parser.h