x86: make e820_end return end_of_ram again for 64bit

even on 64bit systems with less than 4G RAM, we can now use fixmap
to handle acpi SIT near end of ram.

change e820_end to e820_end_of_ram again?
or e820_ram_pfn?
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/e820.c

@@ -1066,10 +1066,8 @@ unsigned long __init e820_end(void)
 		struct e820entry *ei = &e820.map[i];
 		unsigned long end_pfn;
 
-#ifdef CONFIG_X86_32
 		if (ei->type != E820_RAM)
 			continue;
-#endif
 
 		end_pfn = (ei->addr + ei->size) >> PAGE_SHIFT;
 		if (end_pfn > last_pfn)