[POWERPC] Add AT_PLATFORM value for Xilinx Virtex-4 FX

Jakub noticed the cputable.c entry for Xilinx Virtex-4 FX was missing
a .platform value, so the AT_PLATFORM value wouldn't be set correctly.
This adds it.

Signed-off-by: Peter Bergner <bergner@vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index db65c9f..190a57e 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -949,6 +949,7 @@
 			PPC_FEATURE_HAS_MMU | PPC_FEATURE_HAS_4xxMAC,
 		.icache_bsize		= 32,
 		.dcache_bsize		= 32,
+		.platform		= "ppc405",
 	},
 	{	/* 405EP */
 		.pvr_mask		= 0xffff0000,