Installing SMM Gateway SP on the N1SDP may stop the platform from booting
for on-device testing in CI.
In n1sdp.yml, remove `ts-smm-gateway` if it has been added
Keep `ts-smm-gateway` in default SP set so it can still be tested with
`qemu-secureboot`
Signed-off-by: Adam Johnston <adam.johnston@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>