remoteproc: xlnx: Allow single core use in split mode

When operating in split mode, it is a valid usecase to have
only one core enabled in the cluster. Remove exact core count
expecatation from the driver.

Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
Link: https://lore.kernel.org/r/20250618181933.1253033-1-tanmay.shah@amd.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>