qcom: hyp_core_ctl: Add a debugfs interface to set reserve CPUs

The reserve CPUs are initialized via device tree. For testing
purpose provide a debugfs interface to override the default
reserve CPUs.

Change-Id: Ic2a81829212e2ed6b3129d3eac75a8618e5c7c2d
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>