ACPI: arm64: cpuidle: Tolerate platforms with no deep PSCI idle states

Commit cac173bea57d ("ACPI: processor: idle: Rework the handling of
acpi_processor_ffh_lpi_probe()") moved the acpi_processor_ffh_lpi_probe()
call from acpi_processor_setup_cpuidle_dev(), where its return value was
ignored, to acpi_processor_get_power_info(), where it is now treated as
a hard failure. As a result, platforms where psci_acpi_cpu_init_idle()
returned -ENODEV stopped registering any cpuidle states, forcing CPUs to
busy-poll when idle.

On NVIDIA Grace (aarch64) systems with PSCIv1.1, pr->power.count is 1
(only WFI, no deep PSCI states beyond it), so the previous
"count = pr->power.count - 1; if (count <= 0) return -ENODEV;" check
returned -ENODEV for all 72 CPUs and disabled cpuidle entirely.

The lpi_states count is already validated in acpi_processor_get_lpi_info(),
so the check here is redundant. Simplify the loop to iterate over
lpi_states[1..power.count). When only WFI is present, the loop body
simply does not execute and the function returns 0, which is the correct
outcome: there is nothing to validate for FFH and no error to report.

Suggested-by: Huisong Li <lihuisong@huawei.com>
Cc: stable@vger.kernel.org
Fixes: cac173bea57d ("ACPI: processor: idle: Rework the handling of acpi_processor_ffh_lpi_probe()")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>