global: Use proper project name U-Boot (next2)

Use proper project name in README, rst and comment.
Done in connection to commit bb922ca3eb4b ("global: Use proper project name
U-Boot (next)").

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexander Graf <graf@csgraf.de> (ppce500)
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/536af05e7061982f15b668e87f941cdabfa25392.1694157084.git.michal.simek@amd.com
diff --git a/doc/board/xilinx/zynq.rst b/doc/board/xilinx/zynq.rst
index 438912f..76d67bd 100644
--- a/doc/board/xilinx/zynq.rst
+++ b/doc/board/xilinx/zynq.rst
@@ -83,7 +83,7 @@
 ---------------
 
 - Added basic board configurations support.
-- Added zynq u-boot bsp code - arch/arm/mach-zynq
+- Added zynq U-Boot bsp code - arch/arm/mach-zynq
 - Added zynq boards named - zc70x, zed, microzed, zc770_xm010/xm011/xm012/xm013
 - Added zynq drivers: