[ARM] ARMv6: add CPU_HAS_ASID configuration

Presently, we check for the minimum ARM architecture that we're
building for to determine whether we need ASID support.  This is
wrong - if we're going to support a range of CPUs which include
ARMv6 or higher, we need the ASID.

Convert the checks to use a new configuration symbol, and arrange
for ARMv6 and higher CPU entries to select it.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 3c078e3..3278e71 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -85,7 +85,7 @@
   DEFINE(S_OLD_R0,		offsetof(struct pt_regs, ARM_ORIG_r0));
   DEFINE(S_FRAME_SIZE,		sizeof(struct pt_regs));
   BLANK();
-#if __LINUX_ARM_ARCH__ >= 6
+#ifdef CONFIG_CPU_HAS_ASID
   DEFINE(MM_CONTEXT_ID,		offsetof(struct mm_struct, context.id));
   BLANK();
 #endif