ARM: OMAP2+: Add SoC specific map_io functions

Add SoC specific map_io function to be used by the generic DT
board file. This is an intermediate step before having some
generic DT aware map_io function.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>