linux-user: untie syscalls from UID16

Quite a number of uid/gid related syscalls are only defined on systems
with USE_UID16 defined. This is apperently based on the idea that these
system calls would never be called on non-UID16 systems. Make these
syscalls available for all architectures that define them.

drop alpha hack to support selected UID16 syscalls. MIPS and PowerPC
were also defined as UID16, to get uid/gid syscalls available, drop
this error as well.

Change QEMU to reflect this.

Cc: Ulrich Hecht <uli@suse.de>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Alexander Graf <agraf@suse.de>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
