bsp: Update Corstone-1000 firmware settings

Since K3s is not supported for Corstone-1000 and it is been
separated as a cloud-service feature for the Cassini distro in
the meta-cassini repository, which can be included by `k3s.yml`,
the firmware configuration related to this feature doesn't need to be
explicitly removed.

Even if `k3s.yml` is forced to be built with Corstone-1000,
the K3s feature will still be removed, which is defined in
`corstone1000-mps3.yml` on meta-cassini repository.

Further, the `PREFERRED_RPROVIDER` will be set to `no_cloud`
for Corstone-1000.

This relates to the merge request:
https://gitlab.com/Linaro/cassini/meta-cassini/-/merge_requests/199



Signed-off-by: Vikas Katariya <vikas.katariya@arm.com>