arm/PSCI: support PSCI versions greater than 1.0

ATF recently began announcing PSCI v1.1. Since that version is unknown
to u-boot, the PSCI device nodes were not updated.

Switch from the case statement to a greater/less-than comparison so that
v1.1, as well as future versions, get at least the compatible nodes of
known versions.

PSCI v1.1 doesn't seem to have introduced a new corresponding compatible.

Signed-off-by: Andre Heider <a.heider@gmail.com>