dt-bindings: msm: Document "secure debug check action"

Add documentation for "secure debug check action" attribute
in the qcom-ipa node.

Change-Id: If8265318846e0bf1f81b0822e9d339d94199e08d
CRs-Fixed: 2401867
Signed-off-by: Perry Randise <prandise@codeaurora.org>