global: Use proper project name U-Boot

Use proper project name in comments, Kconfig, readmes.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/0dbdf0432405c1c38ffca55703b6737a48219e79.1684307818.git.michal.simek@amd.com

fs/btrfs/compat.h

@@ -46,7 +46,7 @@
 /*
  * Read data from device specified by @desc and @part
  *
- * U-boot equivalent of pread().
+ * U-Boot equivalent of pread().
  *
  * Return the bytes of data read.
  * Return <0 for error.

fs/btrfs/extent-io.h

@@ -8,7 +8,7 @@
  *   Use pointer to provide better alignment.
  * - Remove max_cache_size related interfaces
  *   Includes free_extent_buffer_nocache()
- *   As we don't cache eb in U-boot.
+ *   As we don't cache eb in U-Boot.
  * - Include headers
  *
  * Write related functions are kept as we still need to modify dummy extent