cpuidle: PSCI: Move the `has_lpi` check to the beginning of the function

Currently the first thing checked is whether the PCSI cpu_suspend function
has been initialized.

Another change will be overloading `acpi_processor_ffh_lpi_probe` and
calling it sooner.  So make the `has_lpi` check the first thing checked
to prepare for that change.

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>