lpm_levels: Return true for CPU WFI mode allow check

As it's a general understanding across all architectures to have
a WFI (or equalivalent) mode always present and never disabled
for cpuidle, return true for CPU WFI mode allow check.

Change-Id: Ic55571488f845e4aaf997faaac3b2e0f22368d4e
Signed-off-by: Srinivas Rao L <lsrao@codeaurora.org>