x86: change early_ioremap to use slots instead of nesting

so we could remove the requirement that one needs to call
early_iounmap() in exactly reverse order of early_ioremap().

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/fixmap_32.h b/include/asm-x86/fixmap_32.h
index 784e3e7..8844002 100644
--- a/include/asm-x86/fixmap_32.h
+++ b/include/asm-x86/fixmap_32.h
@@ -94,10 +94,10 @@
 	 * can have a single pgd entry and a single pte table:
 	 */
 #define NR_FIX_BTMAPS		64
-#define FIX_BTMAPS_NESTING	4
+#define FIX_BTMAPS_SLOTS	4
 	FIX_BTMAP_END = __end_of_permanent_fixed_addresses + 256 -
 			(__end_of_permanent_fixed_addresses & 255),
-	FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_NESTING - 1,
+	FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_SLOTS - 1,
 	FIX_WP_TEST,
 #ifdef CONFIG_ACPI
 	FIX_ACPI_BEGIN,