ARM: Allow SoCs to enable scatterlist chaining

Allow SoCs to enable the scatterlist chaining support, which allows
scatterlist tables to be broken up into smaller allocations.

As support for this feature depends on the implementation details of
the users of the scatterlists, we can't enable this globally without
auditing all the users, which is a very big task.  Instead, let SoCs
progressively switch over to using this.

SoC drivers using scatterlists and SoC DMA implementations need
auditing before this option can be enabled for the SoC.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -37,6 +37,9 @@ config ARM
 	  Europe.  There is an ARM Linux project with a web page at
 	  <http://www.arm.linux.org.uk/>.
 
+config ARM_HAS_SG_CHAIN
+	bool
+
 config HAVE_PWM
 	bool
 

arch/arm/include/asm/scatterlist.h

@@ -1,6 +1,10 @@
 #ifndef _ASMARM_SCATTERLIST_H
 #define _ASMARM_SCATTERLIST_H
 
+#ifdef CONFIG_ARM_HAS_SG_CHAIN
+#define ARCH_HAS_SG_CHAIN
+#endif
+
 #include <asm/memory.h>
 #include <asm/types.h>
 #include <asm-generic/scatterlist.h>