omap: igep0020: name refactoring for future merge with IGEP3

IGEP2 and IGEP3 boards are very similar and can be merged into one file.
Start refactoring with changing igep2 to igep where applicable.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Acked-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>