vf_i2c: update I2C controller logic

Update the I2C controller logic to be more consistent with the
newer version of the controller reference manual.
This makes it work better on modern LS/LX platforms and avoids
unnecessary delays. Also fixes a lock leak.

Tested by: bz (LS1088a FDT), Pierre-Luc Drouin (Honeycomb, ACPI)

(cherry picked from commit 44847114bd4c61ed3dfcc879fa0d7deb452e12d3)