MFC r347489-r347491, r347512

r347489:
allwinner: clk: prediv_mux: Init the current parent

Do not init the first parent but read the clock register to find
it's current parent and init this one.

r347490:
allwinner: clk: sun8i_r: Correct resets

The i2c reset wasn't defined and some bits where wrong, correct them.

r347491:
twsi: Calculate the clock param based on the bus frequency

Instead of precalculating the different speed, respect the bus frequency
and calculate the clock register parameter based on it.
If the platform didn't register the core clk, fallback on the precomputed
values (This is likely do be the case on Marvell boards).

r347512:
arm: allwinner: aw_clk_nm: Don't reparent the clock if we didn't ask

When looking for the best frequency don't change the clock parent if the
clock wasn't configured to do that.