stmhal: Add SPI class.

stmhal/Makefile

stmhal/accel.c

stmhal/adc.c

stmhal/dac.c

stmhal/extint.c

stmhal/file.c

stmhal/hal/src/stm32f4xx_hal_spi.c

stmhal/i2c.c

stmhal/led.c

stmhal/main.c

stmhal/modpyb.c

stmhal/pin.c

stmhal/qstrdefsport.h

stmhal/rtc.c

stmhal/servo.c

stmhal/spi.c

stmhal/spi.h