msm: ADSPRPC: Use ID in response to get context pointer

Send context ID in rpc header instead of context pointer.
Validate context ID received in response and get context pointer.

Change-Id: I9cfd10d0c1b25c3085b8e15c7ca1c8ff214bf10d
Acked-by: Viswanatham Paduchuri <vpaduchu@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>