ARM: OMAP: Add helper module for board specific I2C bus registration

This helper module simplifies I2C bus registration for different OMAP
platforms by doing registration in one place only and to allow board
specific bus configuration like clock rate and number of busses configured.

Helper should cover OMAP processors from first to third generation.

This patch just adds the feature and current implementation cleanup and
board file modifications will be done in following patches.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>