Simplify semaphore implementation

By removing the negative values of 'count' and relying on the wait_list to
indicate whether we have any waiters, we can simplify the implementation
by removing the protection against an unlikely race condition.  Thanks to
David Howells for his suggestions.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --cc include/linux/semaphore.h
Simple merge

diff --cc kernel/semaphore.c
Simple merge