x86: Increase RAM_SIZE to 256K

When running with qemu often times the developer want to enable all
sorts of debugs which end up not working with only 192K.

Change-Id: I8d784618b9a0d911944f831a4058b34abc0c3e35
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>