Arndale kernel should use 2/2 memory split by default

The current Arndale kernel, as described on https://wiki.linaro.org/Boards/Arndale/Setup/EnterpriseUbuntuServer, uses a 1/3GB user/kernel memory split. However, the Arndale has 2GB of RAM. This means that half of the board's RAM ends up being "highmem", severely impacting system performance. (It also means that kernel code must explicitly manage mapping in/out of any code/data resident above physical address 0x80000000.)

The default config should be changed to enable CONFIG_VMSPLIT_2G