fixup for ACPI / PPTT: cacheinfo: Label caches based on fw_token

While the PROCESSOR_ID_VALID flag can't be relied on to indicate
the acpi_processor_id field is valid, they aren't _all_ vaild, only
the leaves.

This patch restores the leaf check from the (leaf && valid_flag)
check that was over-zealously removed.

This stops us taking the lowest uninitialsed value (usually 0) in
the intermediate PPTT nodes as being the id for the chhce.

Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: James Morse <james.morse@arm.com>