Board set-up functions should report a fail rather than hang forever

[xross]

If a user runs a project on a custom board it would be nice if the project didn't hang forever on an I2S access.

Instead the func should return error.

Even a trip my be more beneficial to e developer than a hang.

Note, the code appears to be trying to the right thing, but if using Lib_i2c with nothing attached (i.e. no pull up) then lib_i2c will hang forever...

[xross]

On reflection, the "real" fix is likely in lib_i2c. Adding a timeout or checking for pull-up etc.

[xross]

xmos/lib_i2c#97