esp8266 --> esp32

This changes all SPI functions that take data pointers which are
not modified so that the declaration is const. This allows them
to be used with const data (i.e. held in flash). No functional
changes are required.

The defnitions of spiWrite() and spiTransferBytes()  in
esp-hal-spi.h/c have been updated to be consistent.

Tests:
 - Build a simple sketch using SPI.writePattern() and
   SPI.transferBytes()  which uses const data and verify that the
   attached device functions as expected.

fixes: https://github.com/espressif/arduino-esp32/issues/3241

* #1623, implementing suggested change

Splitted suggested fix issue #1623 in a header and source part. Dit not completely dive into the code.
Giving data twice as parameter feels wrong, but it compiles, and i can succesfully use the W5500 with SPI with this fix.
Doesn't compile without.

* #1623, implementing suggested change SPI.h/cpp

Splitted suggested fix issue #1623 in a header and source part. Dit not completely dive into the code.
Giving data twice as parameter feels wrong, but it compiles, and i can succesfully use the W5500 with SPI with this fix.
Doesn't compile without.

* Adding getClockDivider function

* indentation correction

When user selected HSPI with SPIClass name(HSPI) ESP was, by default,
still using VSPI ports (the ones defined in pins_arduino.h).
With this change when user selects HSPI then HSPI default ports will be
used.
If user won't specify HSPI then VSPI default ports will be used.
If user will specify SCLK, MOSI, MISO and SS with SPI.begin() then user
defined ports will be used no matter if VSPI or HSPI is selected.
With this change fe. SD library can use default HSPI ports. It was
possible to
pass HSPI SPI instance to SD lib, however even then it was using VSPI
ports which were (probably) GPIO matrixed to HSPI.

Some boards have different default pins for SPI

Thanks @Ladyada

Use transactions to skip mutex locks for reads and writes