Fix bit-length bugs in Esp32 SPIClass

[kmihaylov]

These functions are added:

	spi_ll_set_dummy(&dev, 0);
	spi_ll_set_command_bitlen(&dev, 0);
	spi_ll_set_addr_bitlen(&dev, 0);

The PR should NOT be merged yet due SPI.read8() not working properly yet. #2437 (comment)

The text below is for my reference.

In Sming/Arch/Esp32/SPI.cpp the main `object` is the SPI device.
This object is spi_signal_conn_t (see esp-idf/components/soc/include/soc/spi_periph.h).
The hardware access is realised through the *hw member of this struct, that is of type
spi_dev_t (see esp-idf/components/soc/esp32/include/soc/spi_struct.h)
The Sming's SPI class uses the esp-idf's initialization functions declarations
in eps-idf/components/hal/esp32/include/hal/spi_ll.h

[mikee47]

@kmihaylov I've revised the title, just remove [WIP] when you're happy with the PR.