tools/insn: Restore the relative include paths for cross building

Building perf on ppc causes:

  In file included from util/intel-pt-decoder/intel-pt-insn-decoder.c:15:
  util/intel-pt-decoder/../../../arch/x86/lib/insn.c:14:10: fatal error: asm/inat.h: No such file or directory
     14 | #include <asm/inat.h> /*__ignore_sync_check__ */
        |          ^~~~~~~~~~~~

Restore the relative include paths so that the compiler can find the
headers.

Fixes: 93281c4a ("x86/insn: Add an insn_decode() API")
Reported-by: NIan Rogers <irogers@google.com>
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Tested-by: NIan Rogers <irogers@google.com>
Tested-by: NStephen Rothwell <sfr@canb.auug.org.au>
Link: https://lkml.kernel.org/r/20210317150858.02b1bbc8@canb.auug.org.au

tools/arch/x86/lib/insn.c

@@ -11,13 +11,13 @@
 #else
 #include <string.h>
 #endif
-#include <asm/inat.h> /*__ignore_sync_check__ */
-#include <asm/insn.h> /* __ignore_sync_check__ */
+#include "../include/asm/inat.h" /* __ignore_sync_check__ */
+#include "../include/asm/insn.h" /* __ignore_sync_check__ */
 
 #include <linux/errno.h>
 #include <linux/kconfig.h>
 
-#include <asm/emulate_prefix.h> /* __ignore_sync_check__ */
+#include "../include/asm/emulate_prefix.h" /* __ignore_sync_check__ */
 
 #define leXX_to_cpu(t, r)						\
 ({									\