mhi: core: check for special events at mission mode entry

In some cases, the special purpose event scheduler may not run
if the interrupt comes close to mission mode entry point and if
no suspend/resume activity follows. Do a check to see if any
pending events need to be processed.

Change-Id: Ic3bf22562f250ec4bb46c14f58617c3b0d5de883
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>