unified/tests: tag working some tests kernel as 'unified_capable'

This allows running the sanitycheck with:

  --tag unified_capable -x KERNEL_TYPE=unified

to run the unified kernel with the tests it is currently known to be
able to run.

Change-Id: Ic145fc6adca162745887672372226fd67447b34a
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>