[ARM] Fix sys_sendto and sys_recvfrom 6-arg syscalls

Rather than providing more wrappers for 6-arg syscalls, arrange for
them to be supported as standard.  This just means that we always
store the 6th argument on the stack, rather than in the wrappers.

This means we eliminate the wrappers for:
* sys_futex
* sys_arm_fadvise64_64
* sys_mbind
* sys_ipc

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>