dt-bindings: Add snapshot of hyp_core_ctl driver documentation

This snapshot is taken from msm-4.14 as of commit 097667ef518f31e
("qcom: hyp_core_ctl: Get reserve CPUs from Hypervisor").

Change-Id: I3754a6b665d62b7517dab57396040035e3adfd40
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>