Fix assembling "isb sy" for aarch64 on LP64BE architectures.
Cherry-picked from upstream:

https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=05cfb0d8cc9b7f8676f5ae55a93642f091d5405f;hp=0ec992e6647c00fc234cdf4c11732b6711b024af

Thanks to ryo@ for fixing and pulling it to upstream!

Index: external/gpl3/binutils/dist/gas/config/tc-aarch64.c
===================================================================
RCS file: /home/netbsd/src/external/gpl3/binutils/dist/gas/config/tc-aarch64.c,v
retrieving revision 1.1.1.6
diff -p -u -r1.1.1.6 tc-aarch64.c
--- external/gpl3/binutils/dist/gas/config/tc-aarch64.c	3 Apr 2020 23:40:11 -0000	1.1.1.6
+++ external/gpl3/binutils/dist/gas/config/tc-aarch64.c	19 Oct 2020 06:53:09 -0000
@@ -250,12 +250,6 @@ set_fatal_syntax_error (const char *erro
 typedef struct
 {
   const char *template;
-  unsigned long value;
-} asm_barrier_opt;
-
-typedef struct
-{
-  const char *template;
   uint32_t value;
 } asm_nzcv;
 
@@ -3994,7 +3988,7 @@ static int
 parse_barrier (char **str)
 {
   char *p, *q;
-  const asm_barrier_opt *o;
+  const struct aarch64_name_value_pair *o;
 
   p = q = *str;
   while (ISALPHA (*q))