Fix CONFIG_NOHIGHMEM for extended crashkernel command line

This patch fixes a build error with CONFIG_KEXEC=y and CONFIG_NOHIGHMEM=y.

linux-2.6-mm$ LANG=C make

  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CALL    scripts/checksyscalls.sh
  CHK     include/linux/compile.h
  CC      arch/i386/kernel/setup.o

arch/i386/kernel/setup.c: In function 'reserve_crashkernel':
arch/i386/kernel/setup.c:391: error: 'highend_pfn' undeclared (first use in this function) arch/i386/kernel/setup.c:391: error: (Each undeclared identifier is reported only once arch/i386/kernel/setup.c:391: error: for each function it appears in.) arch/i386/kernel/setup.c:391: error: 'highstart_pfn' undeclared (first use in this function) make[1]: *** [arch/i386/kernel/setup.o] Error 1
make: *** [arch/i386/kernel] Error 2

---
 arch/i386/kernel/setup.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

@@ -381,6 +381,20 @@ extern unsigned long __init setup_memory
 extern void zone_sizes_init(void);
 #endif /* !CONFIG_NEED_MULTIPLE_NODES */
 
+
+#ifdef CONFIG_HIGHMEM
+static inline unsigned long long get_total_mem(void)
+{
+	return (max_low_pfn + highend_pfn - highstart_pfn) << PAGE_SHIFT;
+}
+#else
+static inline unsigned long long get_total_mem(void)
+{
+	return max_low_pfn << PAGE_SHIFT;
+}
+#endif
+
+
 #ifdef CONFIG_KEXEC
 static void __init reserve_crashkernel(void)
 {

@@ -388,7 +402,7 @@ static void __init reserve_crashkernel(v
 	unsigned long long 	crash_size, crash_base;
 	int			ret;
 
-	free_mem = (max_low_pfn + highend_pfn - highstart_pfn) << PAGE_SHIFT;
+	free_mem = get_total_mem();
 
 	ret = parse_crashkernel(boot_command_line, free_mem,
 			&crash_size, &crash_base);