ARM: OMAP2+: Stop building legacy code for dra7 and omap4/5

With the recent changes we are now booting am3/4, dra7, and omap4/5
without legacy data using devicetree, simple-pm-bus and genpd. Let's not
initialize and build the legacy data unless CONFIG_OMAP_HWMOD is selected
based on the SoCs enabled in .config.

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