ARM: OMAP4+: Remove the un-necessary cache flush from hotplug code

This was added with intial port where OMAP PM support wasn't existing
and only simple WFI based hooks were used.

This should have been cleaned up while adding the PM support but some
how fall through cracks.

So remove the cache flush code which is no longer needed now.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>