seccomp: Get compat syscalls from asm-generic header

Move retrieval of compat syscall numbers into inline function defined in
asm-generic header so that arches may override it.

[ralf@linux-mips.org: Resolve merge conflict.]

Suggested-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: IMG-MIPSLinuxKerneldevelopers@imgtec.com
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12978/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>