Commit 688036b5 removed the function
'shmobile_enter_wfi' but we forgot to remove the definition in the header file.

Note this function is just an alias to 'cpu_do_idle()' wrapped into a cpuidle
function callback prototype which already exists with the default WFI state
and the arm_simple_enter function.

Remove the function prototype.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: NSimon Horman <horms+renesas@verge.net.au>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>