arm64: zynqmp: Do not use '_' in DT node names

Using '_' is not recommended for node names. Use '-' instead.
Pretty much run seds below for node names.
s/heartbeat_led/heartbeat-led/
s/gtr_sel/gtr-sel/
s/zynqmp_ipi/zynqmp-ipi/
s/nvmem_firmware/nvmem-firmware/
s/soc_revision/soc-revision/

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/dd33d6cb0595ffedab117d477f4a3c9d9eb11715.1695808665.git.michal.simek@amd.com