arm: Create proper .rdata sections for COFF

As .rodata isn't one of the default created sections for COFF, it was
created as a read-write data section. By using the default .rdata
section name for COFF, it automatically becomes a read-only data section.
The existing ".section .rodata" works as intended for ELF though.

This is based on an original patch and diagnose by Tom Tan
<Tom.Tan@microsoft.com>.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/aarch64/asm.S

@@ -63,6 +63,8 @@ ELF     .size   \name, . - \name
 .else
         .section        .rodata
 .endif
+#elif defined(_WIN32)
+        .section        .rdata
 #elif !defined(__MACH__)
         .section        .rodata
 #else

libavutil/arm/asm.S

@@ -125,6 +125,8 @@ ELF     .size   \name, . - \name
 .else
         .section        .rodata
 .endif
+#elif defined(_WIN32)
+        .section        .rdata
 #elif !defined(__MACH__)
         .section        .rodata
 #else