arm64: rwsem: use asm-generic rwsem implementation

asm-generic offers an atomic-add based rwsem implementation, which
can avoid the need for heavier, spinlock-based synchronisation on the
fast path.

This patch makes use of the optimised implementation for arm64 CPUs.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit c209f79940)
Signed-off-by: Mark Brown <broonie@linaro.org>

arch/arm64/Kconfig

@@ -69,7 +69,7 @@ config LOCKDEP_SUPPORT
 config TRACE_IRQFLAGS_SUPPORT
 	def_bool y
 
-config RWSEM_GENERIC_SPINLOCK
+config RWSEM_XCHGADD_ALGORITHM
 	def_bool y
 
 config GENERIC_HWEIGHT

arch/arm64/include/asm/Kbuild

@@ -29,6 +29,7 @@ generic-y += pci.h
 generic-y += poll.h
 generic-y += posix_types.h
 generic-y += resource.h
+generic-y += rwsem.h
 generic-y += scatterlist.h
 generic-y += sections.h
 generic-y += segment.h