machine-xilinx-default.inc: Remove use of MACHINE_KCONFIG

* Variable is no longer used

Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
linux/configs: Add config fragment to increase /dev/ram size

* features/blk/dev-ram-32mb.scc: Increases BLK_DEV_RAM_SIZE to 32768 for
  a 32MB RAM block device, whilst reducing the count of devices to 4
* Use the feature fragment as default for Zynq

Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
device-tree.bb: Set package arch to machine arch

* Device trees are built individually for each machine

Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>