[ARM] 5456/1: add sys_preadv and sys_pwritev

Kernel 2.6.30-rc1 added sys_preadv and sys_pwritev to most archs
but not ARM, resulting in

<stdin>:1421:2: warning: #warning syscall preadv not implemented
<stdin>:1425:2: warning: #warning syscall pwritev not implemented

This patch adds sys_preadv and sys_pwritev to ARM.

These syscalls simply take five long-sized parameters, so they
should have no calling-convention/ABI issues in the kernel.

Tested on armv5tel eabi using a preadv/pwritev test program posted
on linuxppc-dev earlier this month.

It would be nice to get this into the kernel before 2.6.30 final,
so that glibc's kernel version feature test for these syscalls
doesn't have to special-case ARM.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>