boot/xilinx-prebuilt: add xilinx_v2025.2 hash

Add hash for xilinx_v2025.2 version, so that example defconfigs can be
bumped to the latest version individually.

Since the license.txt changes with each release, move the hashes to version
specific directories instead of having a generic hash file.

xilinx_v2025.1 hash is moved to boot/xilinx-prebuilt/xilinx_v2025.1_update1
xilinx_v2025.2 hash is added to boot/xilinx-prebuilt/xilinx_v2025.2

Signed-off-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/xilinx-prebuilt/xilinx_v2025.2/xilinx-prebuilt.hash

@@ -0,0 +1,5 @@
+# Locally calculated
+sha256  d292a52ac167631860b5e9a8d8356946289da164ddde4c5393977dc1652dcadb  xilinx-prebuilt-xilinx_v2025.2.tar.gz
+
+# Locally calculated
+sha256  e7ed8599c0cbf9e28d07883f94ee6ff694f6a702daa56c75b2cf4b30105baecc  LICENSE