ARM: OMAP1: Use generic map_io, init_early and init_irq

This allows removing omap hacks for map_io allowing generic
map_io.

Note that in the future we can't do cpu_is_omapxxxx detection
until in init_early. This means that board-innovator.c now
assumes 15xx only, and board-generic.c assumes 16xx only.
This is best fixed later on by passing the SoC type from
device tree.

Signed-off-by: Tony Lindgren <tony@atomide.com>