[ARM] use asm/sections.h

Update to use the asm/sections.h header rather than declaring these
symbols ourselves.  Change __data_start to _data to conform with the
naming found within asm/sections.h.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 4898bdc..0021607 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -119,7 +119,7 @@
 #endif
 
 	.data : AT(__data_loc) {
-		__data_start = .;	/* address in memory */
+		_data = .;		/* address in memory */
 
 		/*
 		 * first, the init task union, aligned