arch/sparc: Introduce cmpxchg_u8 SPARC

arch/sparc: Introduce cmpxchg_u8 SPARC

SPARC supports 32 bit and 64 bit cmpxchg right now. Add support
for 8 bit (1 byte) cmpxchg. This is required to support queued
rwlocks feature  which uses 1 byte cmpxchg.

The function __cmpxchg_u8 here uses the 4 byte cas instruction with a
byte manipulation to achieve 1 byte cmpxchg.

Signed-off-by: Babu Moger <babu.moger@oracle.com>
Reviewed-by: HÃ¥kon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Steve 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 a12ee2349312d7112b9b7c6ac2e70c5ec2ca334e)

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