arm64: zynqmp: Assign TSU clock frequency for GEMs

Allow changing TSU clock for all GEMs. Kria SOM is using this
functionality that's why set TSU clock frequency as 250MHz (minimum when
running at 1G) to allow PTP functionality.

Signed-off-by: Harini Katakam <harini.katakam@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/3b9285b50a2a4abb136ecb0873343a4e84626581.1686228675.git.michal.simek@amd.com