tools uapi: fix RISC-V 64-bit support

The BPF library is not built on 64-bit RISC-V, as the BPF feature is
not detected. Looking more in details, feature/test-bpf.c fails to build
with the following error:

| In file included from /tmp/linux-4.19.12/tools/include/uapi/asm/bitsperlong.h:17,
|                  from /tmp/linux-4.19.12/tools/include/uapi/asm-generic/unistd.h:2,
|                  from /usr/include/riscv64-linux-gnu/asm/unistd.h:1,
|                  from test-bpf.c:2:
| /tmp/linux-4.19.12/tools/include/asm-generic/bitsperlong.h:14:2: error: #error Inconsistent word size. Check asm/bitsperlong.h
|  #error Inconsistent word size. Check asm/bitsperlong.h
|   ^~~~~

The UAPI from the tools directory is missing RISC-V support, therefore
bitsperlong.h from asm-generic is used, defaulting to 32 bits.

Fix that by adding tools/arch/riscv/include/uapi/asm/bitsperlong.h as
a copy of arch/riscv/include/uapi/asm/bitsperlong.h and by updating
tools/include/uapi/asm/bitsperlong.h.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

tools/arch/riscv/include/uapi/asm/bitsperlong.h

+/*
+ * Copyright (C) 2012 ARM Ltd.
+ * Copyright (C) 2015 Regents of the University of California
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _UAPI_ASM_RISCV_BITSPERLONG_H
+#define _UAPI_ASM_RISCV_BITSPERLONG_H
+
+#define __BITS_PER_LONG (__SIZEOF_POINTER__ * 8)
+
+#include <asm-generic/bitsperlong.h>
+
+#endif /* _UAPI_ASM_RISCV_BITSPERLONG_H */

tools/include/uapi/asm/bitsperlong.h

@@ -13,6 +13,8 @@
 #include "../../arch/mips/include/uapi/asm/bitsperlong.h"
 #elif defined(__ia64__)
 #include "../../arch/ia64/include/uapi/asm/bitsperlong.h"
+#elif defined(__riscv)
+#include "../../arch/riscv/include/uapi/asm/bitsperlong.h"
 #else
 #include <asm-generic/bitsperlong.h>
 #endif