arm64: memory: Simplify _VA_START and _PAGE_OFFSET definitions

Rather than subtracting from -1 and then adding 1, we can simply
subtract from 0.
Tested-by: NSteve Capper <steve.capper@arm.com>
Reviewed-by: NSteve Capper <steve.capper@arm.com>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will@kernel.org>

arch/arm64/include/asm/memory.h

@@ -44,8 +44,7 @@
  * VA_START - the first kernel virtual address.
  */
 #define VA_BITS			(CONFIG_ARM64_VA_BITS)
-#define _PAGE_OFFSET(va)	(UL(0xffffffffffffffff) - \
-					(UL(1) << (va)) + 1)
+#define _PAGE_OFFSET(va)	(-(UL(1) << (va)))
 #define PAGE_OFFSET		(_PAGE_OFFSET(VA_BITS))
 #define KIMAGE_VADDR		(MODULES_END)
 #define BPF_JIT_REGION_START	(KASAN_SHADOW_END)
@@ -63,8 +62,7 @@
 #else
 #define VA_BITS_MIN		(VA_BITS)
 #endif
-#define _VA_START(va)		(UL(0xffffffffffffffff) - \
-				(UL(1) << ((va) - 1)) + 1)
+#define _VA_START(va)		(-(UL(1) << ((va) - 1)))
 
 #define KERNEL_START      _text
 #define KERNEL_END        _end