testplan/kms: Make documentation is mandatory for all kms subtests

As testplan documentation is ready for all kms tests, update the
testplan config to make sure we are not missing the documentation
all the kms tests.

Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>