OMAP2+: VC: more registers are per-channel starting with OMAP5

Starting with OMAP5, the following registers are per-channel and not
common to a all VC channels:

 - SMPS I2C slave address
 - SMPS voltage register address offset
 - SMPS cmd/value register address offset
 - VC channel configuration register

Move these from the channel-common struct into the per-channel struct
to support OMAP5.

Signed-off-by: Kevin Hilman <khilman@ti.com>