Unify umount function implementations (bug 16552).

Unify umount function implementations (bug 16552).

Linux kernel architectures have various arrangements for umount
syscalls.  There is a syscall that takes flags, and an older one that
does not.  Newer architectures have only the one taking flags, under
the name umount2 (or under the name umount, in the ia64 case).  Older
architectures may have both, under the names umount2 and umount (or
under the names umount and oldumount, in the alpha case).  glibc then
has several similar implementations of the umount function (no flags)
in terms of either the __umount2 function, or the corresponding
syscall, or in terms of the old syscall under either of its names.

This patch simplifies the implementations in glibc by always using the
__umount2 function to implement the umount function on all systems
using the Linux kernel.  The linux/generic implementation is moved to
sysdeps/unix/sysv/linux (without any changes to code or comments) and
all the other variants are removed.  (This will have the effect of
causing the new syscall to be used in some cases that previously used
the old one, but as discussed for previous changes, such a change to
the underlying syscalls used is OK.)

There remain two variants of how the __umount2 function is
implemented, either in umount2.S, or, for ia64, in syscalls.list.

Tested with build-many-glibcs.py.

	[BZ #16552]
	* sysdeps/unix/sysv/linux/generic/umount.c: Move to ....
	* sysdeps/unix/sysv/linux/umount.c: ... here.
	* sysdeps/unix/sysv/linux/arm/umount.c: Remove file.
	* sysdeps/unix/sysv/linux/hppa/umount.c: Likewise.
	* sysdeps/unix/sysv/linux/ia64/umount.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/umount.c: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/umount.c: Likewise.
	* sysdeps/unix/sysv/linux/umount.S: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/umount.c: Likewise.