This is a massive change, spread across several files.
     - the calibration structure is changed
     - it doesn't live at offset 0x1800 any more
     - it must beloaded by SDB structures (not there yet)
     - all calibration users are fixed
     - calibration.c is a new file dealing with it
     - i2c.c has some material less, because of calibration.c
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>