kernel: i2c padconf workaround

The padconf library runs in user mode, but to actually affect the
padconf register contents, the processor has to be in privileged
mode. A full server based solution will be developed, but for now
just set the pinmux in the kernel at boot.

Change-Id: I170ed54dae64b27cd9bd8807445231598fb8e3e1
i2c: initial bus drivers for am335x and dm37xx

Change-Id: I478704fbf30dbf6d3382bcbfb11e75b512c032a1