drm/msm-hyp: parse client id from dtsi

Read client id from dtsi, then parse and return it when queried
by user space. This change allows setting different client id
without changing driver code.

Change-Id: I3858ee80748f2a485a115c652608cc484d6f3720
Signed-off-by: Camus Wong <camusw@codeaurora.org>