signal: Remove the need for __ARCH_SI_PREABLE_SIZE and SI_PAD_SIZE

Rework the defintion of struct siginfo so that the array padding
struct siginfo to SI_MAX_SIZE can be placed in a union along side of
the rest of the struct siginfo members.  The result is that we no
longer need the __ARCH_SI_PREAMBLE_SIZE or SI_PAD_SIZE definitions.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

arch/riscv/include/uapi/asm/Kbuild

@@ -26,3 +26,4 @@ generic-y += swab.h
 generic-y += termbits.h
 generic-y += termios.h
 generic-y += types.h
+generic-y += siginfo.h

arch/riscv/include/uapi/asm/siginfo.h

@@ -1,24 +0,0 @@
-/*
- * Copyright (C) 2012 ARM Ltd.
- * Copyright (C) 2016 SiFive, Inc.
- *
- * 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 __ASM_SIGINFO_H
-#define __ASM_SIGINFO_H
-
-#define __ARCH_SI_PREAMBLE_SIZE	(__SIZEOF_POINTER__ == 4 ? 12 : 16)
-
-#include <asm-generic/siginfo.h>
-
-#endif