main: use sdeventplus wrapper

Convert sdevent to new C++ library wrappers.

Tested: ran on hardware platform and observed snooper able to collect
POST codes. Unit tests still pass.

Change-Id: Ic69a41fc20dd77595f065600633a1dcfafd44a5a
Signed-off-by: Kun Yi <kunyi@google.com>
3 files changed