uboot-zynq: fix dtc compilation on host gcc 10

gcc 10 defaults to -fno-common, which causes an error
when linking.

Back-port the following Linux kernel commit to fix it:
e33a814e772c (scripts/dtc: Remove redundant YYLOC global declaration)

Tested on an Arch Linux host with gcc 10.1.0

Signed-off-by: Luis Araneda <luaraneda@gmail.com>
(cherry picked from commit 8b870418f1)

package/boot/uboot-zynq/patches/010-fix_dtc_compilation_on_host_gcc10.patch

@@ -0,0 +1,46 @@
+From e33a814e772cdc36436c8c188d8c42d019fda639 Mon Sep 17 00:00:00 2001
+From: Dirk Mueller <dmueller@suse.com>
+Date: Tue, 14 Jan 2020 18:53:41 +0100
+Subject: [PATCH] scripts/dtc: Remove redundant YYLOC global declaration
+
+gcc 10 will default to -fno-common, which causes this error at link
+time:
+
+  (.text+0x0): multiple definition of `yylloc'; dtc-lexer.lex.o (symbol from plugin):(.text+0x0): first defined here
+
+This is because both dtc-lexer as well as dtc-parser define the same
+global symbol yyloc. Before with -fcommon those were merged into one
+defintion. The proper solution would be to to mark this as "extern",
+however that leads to:
+
+  dtc-lexer.l:26:16: error: redundant redeclaration of 'yylloc' [-Werror=redundant-decls]
+   26 | extern YYLTYPE yylloc;
+      |                ^~~~~~
+In file included from dtc-lexer.l:24:
+dtc-parser.tab.h:127:16: note: previous declaration of 'yylloc' was here
+  127 | extern YYLTYPE yylloc;
+      |                ^~~~~~
+cc1: all warnings being treated as errors
+
+which means the declaration is completely redundant and can just be
+dropped.
+
+Signed-off-by: Dirk Mueller <dmueller@suse.com>
+Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
+[robh: cherry-pick from upstream]
+Cc: stable@vger.kernel.org
+Signed-off-by: Rob Herring <robh@kernel.org>
+---
+ scripts/dtc/dtc-lexer.l | 1 -
+ 1 file changed, 1 deletion(-)
+
+--- a/scripts/dtc/dtc-lexer.l
++++ b/scripts/dtc/dtc-lexer.l
+@@ -38,7 +38,6 @@ LINECOMMENT	"//".*\n
+ #include "srcpos.h"
+ #include "dtc-parser.tab.h"
+ 
+-YYLTYPE yylloc;
+ extern bool treesource_error;
+ 
+ /* CAUTION: this will stop working if we ever use yyless() or yyunput() */