arch_topology: Drop unnecessary check for uninitialised package_id

With the support of socket node parsing from the device tree and
assigning 0 as package_id in absence of socket nodes, there is no need
to check for invalid package_id. It is always initialised to 0 or values
from the device tree socket nodes.

Just drop that now redundant check for uninitialised package_id.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>