i2c: sunxi: Support every i2c controller on each supported platform

Changes since v4:
* Got rid of Kconfig after all
* Only build mvtwsi when at least one controller is enabled on sunxi
* Controller 0 doesn't have to be enabled in particular

Changes since v3:
* Kconfig support for MVTWSI
* Only enable twsi0 by default for platforms that always use it for the AXP
* Remove enabling other I2C busses by default on boards that expose them on pin headers since those might be used for some other functionalities

Changes since v2:
* I2C/TWI busses enable for Cubietruck as well

Changes since v1:
* Kconfig option to enable I2C/TWI controllers 1-4 (when applicable)
* Following patch to enable exposed busses on a few community-supported single-board-computers

This series adds support for every i2c controller found on sun4i/sun5i/sun6i/sun7i/sun8i platforms and shouldn't break support for Marvell platforms (orion5x, kirkwood, armada xp) the driver was originally written for.

Regarding sunxi, I double-checked that this doesn't conflict with VIDEO_LCD_PANEL_I2C.

I would be interested in having this tested on sun8i (A23), since I changed TWI0 muxing (to PH2-PH3 instead of PB0-PB1), according to the user manual and what is being done on the upstream Linux kernel. I2C was either not working before, or it was being muxed correctly by the bootrom, probably to communicate with the AXP, which luckily made it work in U-Boot too, since the I/O base address was already correct.

My use case here is that I'm writing a slave-side bitbang i2c implementation (with an Arduino) for a school project, using a Cubieboard2 as master and U-Boot as POC. However, only TWI1 was available through the expansion pins, hence the need for this series.