[MIPS] Use SYSVIPC_COMPAT to fix various problems on N32

[MIPS] Use SYSVIPC_COMPAT to fix various problems on N32

N32 SysV IPC system calls should use 32-bit compatible code.
arch/mips/kernel/linux32.c have similar compatible code for O32, but
ipc/compat.c seems more complete.  We can use it for both N32 and O32.

This patch should fix these problems (and other possible problems):

http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=1149188824.6986.6.camel%40diimka-laptop
http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=44C6B829.8050508%40caviumnetworks.com

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>