firmware: arm_ffa: Handle the presence of host partition in the partition info

Currently it is assumed that the firmware doesn't present the host
partition in the list of partitions presented as part of the response
to PARTITION_INFO_GET from the firmware. However, there are few
platforms that prefer to present the same in the list of partitions.
It is not manadatory but not restricted as well.

So handle the same by making sure to check the presence of the host
VM ID in the XArray partition information maintained/managed in the
driver before attempting to add it.

Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
Message-Id: <20250217-ffa_updates-v3-7-bd1d9de615e7@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>