am335x: make get_board_rev() function weak

Current get_board_rev() function returns a hard coded value which is
obviously incorrect for the majority of boards.
Allow boards to provide a correct implementation by making this
function weak.
In addition open code the trivial and useless BOARD_REV_ID define and
adjust the comment.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Cc: Tom Rini <trini@ti.com>

arch/arm/cpu/armv7/am33xx/sys_info.c

@@ -18,6 +18,7 @@
 #include <asm/arch/cpu.h>
 #include <asm/arch/clock.h>
 #include <power/tps65910.h>
+#include <linux/compiler.h>
 
 struct ctrl_stat *cstat = (struct ctrl_stat *)CTRL_BASE;
 
@@ -51,11 +52,11 @@ u32 get_cpu_type(void)
 
 /**
  * get_board_rev() - setup to pass kernel board revision information
- * returns:(bit[0-3] sub version, higher bit[7-4] is higher version)
+ * returns: 0 for the ATAG REVISION tag value.
  */
-u32 get_board_rev(void)
+u32 __weak get_board_rev(void)
 {
-	return BOARD_REV_ID;
+	return 0;
 }
 
 /**

arch/arm/include/asm/arch-am33xx/sys_proto.h

@@ -14,8 +14,6 @@
 #include <asm/ti-common/sys_proto.h>
 #include <asm/arch/cpu.h>
 
-#define BOARD_REV_ID	0x0
-
 u32 get_cpu_rev(void);
 u32 get_sysboot_value(void);