gateware/icE1usb: Use custom I2C core by default rather than SB_I2C

SB_I2C is apparently just a pain to use and buggy and such, so
use our custom one.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: I1596ccbf03dd4450f519fe9b54a7fece125a7fbc
1 file changed