qseecom: change check_blocked flag to an u32 value

Change app entry's check_blocked flag to u32 to indicate the
total number of clients being blocked on this app; then this
app can only be unloaded if this flag is 0.

Change-Id: I0370b25657b6dfdc40a738c784e601907c9b4dd4
Signed-off-by: Zhen Kong <zkong@codeaurora.org>