x86: clean up reserve_bootmem_generic() and port it to 32-bit

1. add reserve_bootmem_generic for 32bit
2. change len to unsigned long
3. make early_res_to_bootmem to use it

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/e820.c

@@ -635,7 +635,7 @@ void __init early_res_to_bootmem(u64 start, u64 end)
 			continue;
 		printk(KERN_INFO "  early res: %d [%llx-%llx] %s\n", i,
 			final_start, final_end - 1, r->name);
-		reserve_bootmem(final_start, final_end - final_start,
+		reserve_bootmem_generic(final_start, final_end - final_start,
 				BOOTMEM_DEFAULT);
 	}
 }