omap: Start using CONFIG_SOC_OMAP

We want to have just CONFIG_ARCH_OMAP2, 3 and 4. The rest
are nowadays just subcategories of these.

Search and replace the following:

ARCH_OMAP2420		SOC_OMAP2420
ARCH_OMAP2430		SOC_OMAP2430
ARCH_OMAP3430		SOC_OMAP3430

No functional changes.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Thomas Weber <weber@corscience.de>
Acked-by: Sourav Poddar <sourav.poddar@ti.com>