mc13xxx: add I2C support (now with regmap), V4

[Marc Reilly]

Hi,

This series (against mfd-2.6/for-next) changes the mc13xxx driver to use 
regmap and adds I2C support.
It has a compile dependency on regmap/for-next, as the spi driver uses the
recently added pad_bits config field.

Changes since V3:
- spi driver uses padded register format (reads should actually work now!)
- mc13873 removed from I2C driver
- fix memory leak on probe error

Cheers,
Marc

PS. Mark Brown added his "reviwed-by" (sic) for what is now 2/4. I've not 
included it here because 1. it changed (albeit very slightly) so I don't 
know if it's bad ettiquie to include it again, and 2. I'm ignorant of the
correct process/way to include it.