qcom: minidump: don't register idle task's stack in minidump

Idle task stacks are not much useful for debug in minidump.
Remove idle task and its stack registration to optimize minidump
size and collection time.

Change-Id: Ifa9e3ba54a6a0c912aa022707496c8f2e48dee02
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>