trace: tegra: nvpower: fix build error

trace: tegra: nvpower: fix build error

is_idle_task is used without including sched.h. Build fails
as declaration is not available. This patch fixes the issue.

Enabling 64K page support exposed this error.

Bug 1526131

Change-Id: I59b37b9dc618a159db0befa79486aeffe5444572
Signed-off-by: Sri Krishna chowdary K <schowdary@nvidia.com>
Reviewed-on: http://git-master/r/676532
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Prashant Gaikwad <pgaikwad@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>