Use correct spelling of "U-Boot"

Correct spelling of "U-Boot" shall be used in all written text
(documentation, comments in source files etc.).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>

lib/Kconfig

@@ -16,7 +16,7 @@ config USE_PRIVATE_LIBGCC
 	depends on HAVE_PRIVATE_LIBGCC
 	help
 	  This option allows you to use the built-in libgcc implementation
-	  of U-boot instead of the one privided by the compiler.
+	  of U-Boot instead of the one privided by the compiler.
 	  If unsure, say N.
 
 config SYS_HZ

lib/zlib/inffast.c

@@ -3,7 +3,7 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
-/* U-boot: we already included these
+/* U-Boot: we already included these
 #include "zutil.h"
 #include "inftrees.h"
 #include "inflate.h"

lib/zlib/inftrees.c

@@ -3,7 +3,7 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
-/* U-boot: we already included these
+/* U-Boot: we already included these
 #include "zutil.h"
 #include "inftrees.h"
 */

lib/zlib/zutil.h

@@ -95,7 +95,7 @@ extern const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 
 /* Diagnostic functions */
 #ifdef DEBUG
-/* Not valid for U-boot
+/* Not valid for U-Boot
 #  include <stdio.h> */
    extern int z_verbose;
    extern void z_error    OF((char *m));