Timeout on SERCOM I2C functions

[awatterott]

We are currently testing a timeout implementation (without timer/interrupts) for the SERCOM I2C functions, because we saw that the SAMD21 can freeze on communication errors or hardware problems. The implementation also fixes the recursion problem in startTransmissionWIRE().

Changes: awatterott@64b6fca

[awatterott]

Our testings have not shown any issues and everything works as expected.
Can I open a PR or should we change anything?