arm-bsp-extras/firmware-fvp-rd-aspen: Remove SCP and SI1+2

Aspen will not contain an SCP. Additionally, Aspen r0
will only have a single SI cluster. So, remove the binaries from the
flash image and updating the remaining offsets.

Also remove the SAFETY_ISLAND_Cx_RECIPE and SAFETY_ISLAND_Cx_IMAGE
variables.

Signed-off-by: Peter Hoyes <peter.hoyes@arm.com>