backports: add generic semaphore.h

backports: add generic semaphore.h

Matthew generalized the semaphore implementation and part of
that collateral evolution consisted of changing the header
used for the expected routines from asm/semaphore.h to
linux/semaphore.h.

mcgrof@garbanzo ~/linux-next (git::master)$ git describe --contains \
	64ac24e738823161693bf791f87adc802cf529ff
v2.6.26-rc1~1155^2~5

commit 64ac24e738823161693bf791f87adc802cf529ff
Author: Matthew Wilcox <matthew@wil.cx>
Date:   Fri Mar 7 21:55:58 2008 -0500

    Generic semaphore implementation

    Semaphores are no longer performance-critical, so a generic C
    implementation is better for maintainability, debuggability and
    extensibility.  Thanks to Peter Zijlstra for fixing the lockdep
    warning.  Thanks to Harvey Harrison for pointing out that the
    unlikely() was unnecessary.

    Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
    Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>