arch/tile/Kconfig: don't specify CONFIG_PAGE_OFFSET for 64-bit builds

It's fixed at half the VA space and there's no point in configuring it.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/Kconfig

@@ -243,6 +243,7 @@ endchoice
 
 config PAGE_OFFSET
 	hex
+	depends on !64BIT
 	default 0xF0000000 if VMSPLIT_3_75G
 	default 0xE0000000 if VMSPLIT_3_5G
 	default 0xB0000000 if VMSPLIT_2_75G