powerpc: Remove unused CPU_FTR_IABR

We removed the last usage of CPU_FTR_IABR in commit 1ad7d705
"powerpc/xmon: Enable HW instruction breakpoint on POWER8".

Mark it as free.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/cputable.h

@@ -165,7 +165,7 @@ extern const char *powerpc_base_platform;
 #define CPU_FTR_ARCH_201		LONG_ASM_CONST(0x0000000200000000)
 #define CPU_FTR_ARCH_206		LONG_ASM_CONST(0x0000000400000000)
 #define CPU_FTR_ARCH_207S		LONG_ASM_CONST(0x0000000800000000)
-#define CPU_FTR_IABR			LONG_ASM_CONST(0x0000001000000000)
+/* Free					LONG_ASM_CONST(0x0000001000000000) */
 #define CPU_FTR_MMCRA			LONG_ASM_CONST(0x0000002000000000)
 #define CPU_FTR_CTRL			LONG_ASM_CONST(0x0000004000000000)
 #define CPU_FTR_SMT			LONG_ASM_CONST(0x0000008000000000)