arm64: add PSCI CPU_SUSPEND based cpu_suspend support

arm64: add PSCI CPU_SUSPEND based cpu_suspend support

This patch implements the cpu_suspend cpu operations method through
the PSCI CPU_SUSPEND API. The PSCI implementation translates the idle state
index passed by the cpu_suspend core call into a valid PSCI state according to
the PSCI states initialized at boot by the PSCI suspend backend.

Entry point is set to cpu_resume physical address, that represents the
default kernel execution address following a CPU reset.

Idle state indices missing a DT node description are initialized to power
state standby WFI so that if called by the idle driver they provide the
default behaviour.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Mark Brown <broonie@linaro.org>