soc: qcom: irq-helper: Add comments to exposed APIs

Add comments and might_sleep() to warn that irq_blacklist_on/off
APIs should not be called in atomic context.

CRs-Fixed: 1063719
Change-Id: Ie6858243a666aeb21cc486208b9dd8221e9ad674
Signed-off-by: Runmin Wang <runminw@codeaurora.org>