arm64: zynqmp: Rename ams_ps/pl node names

Fix child node names to be aligned with dt-binding available in the Linux
kernel which requires names as ams-ps@ and ams-pl@.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/8f1451d614f654cb0d0da1e799e876c078fbf2c9.1688992653.git.michal.simek@amd.com