Hikey960: Change to use recommended power state id format

Hikey960: Change to use recommended power state id format

ARM Power State Coordination Interface (ARM DEN 0022D) chapter
6.5 "Recommended StateID Encoding" defines the state ID which can be
used by platforms. The recommended power states can be presented by
below values; and it divides into three fields, every field has 4 bits
to present power states corresponding to core level, cluster level and
system level.

  0: Run
  1: Standby
  2: Retention
  3: Powerdown

This commit changes to use upper recommended power states definition on
Hikey960; and changes the power state validate function to check the
power state passed from kernel side.

Signed-off-by: Leo Yan <leo.yan@linaro.org>