msm: adsprpc: Check fastrpc channel and context during map and unmap

Check if the fastrpc channel and context is created before during
map and unmap. Also check for dsp process to be initialized.

Change-Id: I0d7195e28e5185dc8d3394d8d1c24b4ec35f7d46
Acked-by: Himateja Reddy <hmreddy@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>