tile: double default VMALLOC space

With per-cpu data as well as loaded kernel modules coming from
the vmalloc arena, we get close to the line all the time and
occasionally need more than we had, so just double it up by default.
Signed-off-by: NChris Metcalf <cmetcalf@tilera.com>

arch/tile/Kconfig

@@ -361,7 +361,7 @@ config CMDLINE_OVERRIDE
 
 config VMALLOC_RESERVE
 	hex
-	default 0x1000000
+	default 0x2000000
 
 config HARDWALL
 	bool "Hardwall support to allow access to user dynamic network"