MKR boards: I2C to sercom2, SPI1 + Serial2 to sercom4

[sandeepmistry]

This pull request changes the sercom used for I2C and SPI1/Serial2, so that sercom can be used for alternative purposes.

-> I2C: from sercom 0 to 2
-> SPI: from sercom 2 to 4

We'll have to be super careful and test the changes on all MKR board types.

@Rocketct if you have some time this week please test this out.

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b200_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request MKR boards: I2C to sercom2, SPI1 + Serial2 to sercom4 #378
5. Select one of the boards under SAMD Pull Request MKR boards: I2C to sercom2, SPI1 + Serial2 to sercom4 #378 in Tools->Board menu
6. Compile/Upload as usual

[Rocketct]

@sandeepmistry tested both SPI and I2C by using the examples of each boards and a I2C sensors and all goes fine, ok for me

[sslupsky]

What is the purpose of this change? The OP says "so that sercom can be used for alternative purposes". What "alternative purposes" are you referring to?

[sandeepmistry]

What "alternative purposes" are you referring to?

Adding an additional SPI interface on pins A3 + A4 to use in conjunction with the new MKR RGB shield.

[henklaak]

Late to the game, but the labels in the MKRWiFi1010V2.0 schematics (ABX00023-schematics.pdf) still reflect the old sercom numbers. Confused me no end (was there a board revision I had missed?), until I traced back this commit and the reasoning behind it (which helped me a lot in fact, as I needed two extra sercoms on the digital pins badly, so thanks!).

Don't know where else I should report docs issues....