arch/sparc: Introduce xchg16 for SPARC

arch/sparc: Introduce xchg16 for SPARC

SPARC supports 32 bit and 64 bit xchg right now. Add the support
for 16 bit (2 byte) xchg. This is required to support queued spinlock
feature which uses 2 byte xchg. This is achieved using 4 byte cas
instructions with byte manipulations.

Also re-arranged the code to call __cmpxchg_u32 inside xchg16.

Signed-off-by: Babu Moger <babu.moger@oracle.com>
Reviewed-by: HÃ¥kon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 79d39e2bab60d18a68a5abc00be4506864397efc)

Conflicts:

	arch/sparc/include/asm/cmpxchg_64.h

Orabug: 26183741
Signed-off-by: Allen Pais <allen.pais@oracle.com>