ARM: OMAP2+: PMU: Remove unused header

Commit 2ac29a14 (ARM: PMU: fix runtime PM enable) moved the call to
pm_runtime_enable() from the OMAP2+ PMU code into the ARM PERF core
code. However, header for pm_runtime which should have been removed
from the OMAP2+ PMU code was not. It is no longer necessary to include
this header in the OMAP2+ PMU code and so remove it.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>