firmware: arm_scpi: improve info message for pre-1.0 firmware

On legacy pre-1.0 firmware versions so far the following message is
printed which may cause some confusion:
SCP Protocol 0.0 Firmware 0.0.0 version

Therefore replace the message with the following if firmware doesn't
provide usable version information:
SCP Protocol legacy pre-1.0 firmware

Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>