qseecom:  Add checks for send_cmd inputs

Improve user input validation across send cmd APIs. Add new
API  __validate_send_cmd_inputs() to validate all user provided
inputs.

Change-Id: Ibbb0c0e7e5483f653bd59b927562b63c1e43c365
Signed-off-by: Mona Hossain <mhossain@codeaurora.org>