Select SCMI/SDS drivers by default on Juno

The SCP binaries provided in the 17.10 Linaro release (and onwards)
have migrated to the SCMI/SDS protocols. Therefore, the ARM TF should
now use the corresponding drivers by default.

This patch changes the default value of the CSS_USE_SCMI_SDS_DRIVER
build option to 1 for Juno.

Change-Id: Idb7e3c6af582f49e332167a2158703c2d781b437
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>