MIPS: ip22: Fix ip28 build for modern gcc

kernelci reports a failure of the ip28_defconfig build after upgrading its
gcc version:

arch/mips/sgi-ip22/Platform:29: *** gcc doesn't support needed option -mr10k-cache-barrier=store.  Stop.

The problem apparently is that the -mr10k-cache-barrier=store option is now
rejected for CPUs other than r10k. Explicitly including the CPU in the
check fixes this and is safe because both options were introduced in
gcc-4.4.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15049/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/sgi-ip22/Platform

@@ -25,7 +25,7 @@ endif
 # Simplified: what IP22 does at 128MB+ in ksegN, IP28 does at 512MB+ in xkphys
 #
 ifdef CONFIG_SGI_IP28
-  ifeq ($(call cc-option-yn,-mr10k-cache-barrier=store), n)
+  ifeq ($(call cc-option-yn,-march=r10000 -mr10k-cache-barrier=store), n)
       $(error gcc doesn't support needed option -mr10k-cache-barrier=store)
   endif
 endif