[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>

arch/arm/mm/Kconfig

@@ -351,6 +351,7 @@ config CPU_V6
 	select CPU_CACHE_V6
 	select CPU_CACHE_VIPT
 	select CPU_CP15_MMU
+	select CPU_HAS_ASID
 	select CPU_COPY_V6 if MMU
 	select CPU_TLB_V6 if MMU
 
@@ -376,6 +377,7 @@ config CPU_V7
 	select CPU_CACHE_V7
 	select CPU_CACHE_VIPT
 	select CPU_CP15_MMU
+	select CPU_HAS_ASID
 	select CPU_COPY_V6 if MMU
 	select CPU_TLB_V6 if MMU
 
@@ -498,6 +500,12 @@ config CPU_TLB_V6
 
 endif
 
+config CPU_HAS_ASID
+	bool
+	help
+	  This indicates whether the CPU has the ASID register; used to
+	  tag TLB and possibly cache entries.
+
 config CPU_CP15
 	bool
 	help