The qemu_sbsa platform uses 42bit address size but
the cortex-a53 only supports 40bit addressing, the
cpu is incompatible with the platform.

The aem_generic is also not used with qemu_sbsa, in
fact, the platform currently only properly supports
the cortex-a57 cpu.

Change-Id: I91c92533116f1c3451d01ca99824e91d3d58df14
Signed-off-by: Tomas Pilar <tomas@nuviateam.com>