ARM: 5897/1: spinlock: don't use deprecated barriers on ARMv7

On ARMv7, the use of the cp15 operations for barriers is deprecated
in favour of the isb, dsb, and dmb instructions.  Change the locking
functions to use the appropriate type of dsb for the architecture
being built for.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>