cmd: Convert existing long help messages to the new macro

- Generally we just drop the #ifdef CONFIG_SYS_LONGHELP and endif lines
  and use U_BOOT_LONGHELP to declare the same variable name as before
- In a few places, either rename the variable to follow convention or
  introduce the variable as it was being done inline before.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/cat.c b/cmd/cat.c
index b059080..18aa6ca 100644
--- a/cmd/cat.c
+++ b/cmd/cat.c
@@ -60,11 +60,9 @@
 	return 0;
 }
 
-#ifdef CONFIG_SYS_LONGHELP
-static char cat_help_text[] =
+U_BOOT_LONGHELP(cat,
 	"<interface> <dev[:part]> <file>\n"
-	"  - Print file from 'dev' on 'interface' to standard output\n";
-#endif
+	"  - Print file from 'dev' on 'interface' to standard output\n");
 
 U_BOOT_CMD(cat, 4, 1, do_cat,
 	   "Print file to standard output",