arm64: Simplify NR_FIX_BTMAPS calculation

We choose NR_FIX_BTMAPS such that each slot (NR_FIX_BTMAPS * PAGE_SIZE)
can address 256K.

Use division to derive NR_FIX_BTMAPS rather than defining it for each
page size.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NSuzuki K. Poulose <suzuki.poulose@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/fixmap.h

@@ -17,6 +17,7 @@
 
 #ifndef __ASSEMBLY__
 #include <linux/kernel.h>
+#include <linux/sizes.h>
 #include <asm/boot.h>
 #include <asm/page.h>
 
@@ -55,11 +56,7 @@ enum fixed_addresses {
 	 * Temporary boot-time mappings, used by early_ioremap(),
 	 * before ioremap() is functional.
 	 */
-#ifdef CONFIG_ARM64_64K_PAGES
-#define NR_FIX_BTMAPS		4
-#else
-#define NR_FIX_BTMAPS		64
-#endif
+#define NR_FIX_BTMAPS		(SZ_256K / PAGE_SIZE)
 #define FIX_BTMAPS_SLOTS	7
 #define TOTAL_FIX_BTMAPS	(NR_FIX_BTMAPS * FIX_BTMAPS_SLOTS)