[ARM] Reliably update SIZEOF_MACHINE_DESC

Generate SIZEOF_MACHINE_DESC using asm-offsets method rather than
relying on people updating the definition in asm/mach/arch.h

arch/arm/kernel/asm-offsets.c

@@ -12,6 +12,7 @@
  */
 #include <linux/sched.h>
 #include <linux/mm.h>
+#include <asm/mach/arch.h>
 
 /*
  * Make sure that the compiler and target are compatible.
@@ -59,5 +60,7 @@ int main(void)
   DEFINE(PAGE_SZ,	       	PAGE_SIZE);
   BLANK();
   DEFINE(SYS_ERROR0,		0x9f0000);
+  BLANK();
+  DEFINE(SIZEOF_MACHINE_DESC,	sizeof(struct machine_desc));
   return 0; 
 }

arch/arm/kernel/head.S

@@ -17,7 +17,6 @@
 #include <asm/mach-types.h>
 #include <asm/procinfo.h>
 #include <asm/ptrace.h>
-#include <asm/mach/arch.h>
 
 /*
  * We place the page tables 16K below TEXTADDR.  Therefore, we must make sure

include/asm-arm/mach/arch.h

@@ -8,12 +8,6 @@
  * published by the Free Software Foundation.
  */
 
-/*
- * The size of struct machine_desc
- *   (for assembler code)
- */
-#define SIZEOF_MACHINE_DESC	52
-
 #ifndef __ASSEMBLY__
 
 struct tag;