i2c-bfin-twi: Disable BF54x support for now

The i2c-bfin-twi driver doesn't support BF54x for now due to
missing header definitions causing the build to fail. Exclude
it for now, it will be enabled again later.

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>