ARM: OMAP2+: Clean up omap4_local_timer_init

Inspired by a patch from Felipe Balbi <balbi@ti.com>, we can
now get rid of most the code in omap4_local_timer_init.

Omap4 is now device tree only.. And we have not properly supported
omap4 ES1.0 revision for a really long time AFAIK.

Let's just remove all that code to simplify things. This assumes
we have arm,cortex-a9-twd-timer entry in the omap4.dtsi file, which
we do.

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