MIPS: Support extended ASIDs

Add support for extended ASIDs as determined by the Config4.AE bit.
Since the only supported CPUs known to implement this are Netlogic XLP
and MIPS I6400, select this variable ASID support based upon
CONFIG_CPU_XLP and CONFIG_CPU_MIPSR6.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Jayachandran C. <jchandra@broadcom.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13211/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -1706,6 +1706,7 @@ config CPU_XLP
 	select CPU_HAS_PREFETCH
 	select CPU_MIPSR2
 	select CPU_SUPPORTS_HUGEPAGES
+	select MIPS_ASID_BITS_VARIABLE
 	help
 	  Netlogic Microsystems XLP processors.
 endchoice
@@ -2001,6 +2002,7 @@ config CPU_MIPSR6
 	bool
 	default y if CPU_MIPS32_R6 || CPU_MIPS64_R6
 	select HAVE_ARCH_BITREVERSE
+	select MIPS_ASID_BITS_VARIABLE
 	select MIPS_SPRAM
 
 config EVA
@@ -2457,9 +2459,13 @@ config MIPS_ASID_SHIFT
 
 config MIPS_ASID_BITS
 	int
+	default 0 if MIPS_ASID_BITS_VARIABLE
 	default 6 if CPU_R3000 || CPU_TX39XX
 	default 8
 
+config MIPS_ASID_BITS_VARIABLE
+	bool
+
 #
 # - Highmem only makes sense for the 32-bit kernel.
 # - The current highmem code will only work properly on physically indexed