cpuidle: menu: Remove the unused get_loadavg function

The fuction get_loadavg was unused and this also caused
a warning during build. This change also removes it from
the allowed warnings white-list.

Change-Id: I85b184e1eb0ab8b3cf763cab87a30e140d00332b
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>