cbus: mark dependencies for ARCH_OMAP

This is just a temporary commit. Ideally, all
these drivers wouldn't depend on a particular
architecture, but some of those Retu/Tahvo
children are using headers under <plat>, so
we must add this dependency until that's sorted
out.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>