MIPS: Only set cpu_has_mmips if SYS_SUPPORTS_MICROMIPS

As Jonas Gorske said in his patch:

   Disable cpu_has_mmips for everything but SEAD3 and MALTA. Most of
   these platforms are from before the micromips introduction, so they
   are very unlikely to implement it.

   Reduces an -Os compiled, uncompressed kernel image by 8KiB for
   BCM63XX.

This patch taks a different approach than his, we gate the runtime
test for microMIPS by the config symbol SYS_SUPPORTS_MICROMIPS.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: Jonas Gorski <jogo@openwrt.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5327/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/cpu-features.h

@@ -109,7 +109,11 @@
 #define cpu_has_rixi		(cpu_data[0].options & MIPS_CPU_RIXI)
 #endif
 #ifndef cpu_has_mmips
-#define cpu_has_mmips		(cpu_data[0].options & MIPS_CPU_MICROMIPS)
+# ifdef CONFIG_SYS_SUPPORTS_MICROMIPS
+#  define cpu_has_mmips		(cpu_data[0].options & MIPS_CPU_MICROMIPS)
+# else
+#  define cpu_has_mmips		0
+# endif
 #endif
 #ifndef cpu_has_vtag_icache
 #define cpu_has_vtag_icache	(cpu_data[0].icache.flags & MIPS_CACHE_VTAG)