Do not pass the MACHINE variable to sub-makes

Do not pass the MACHINE variable to sub-makes or to other
sub-processes through the environment.  Various sub-projects also
define and use a variable called MACHINE for a completely different
purpose.
Improve eth0 link up detection

The link up detection mechanism inspects the "operstate" of the
network interface in question.  Some Ethernet drivers do not fully
implement the "operstate" -- as such, the appropriate states for
determining link-up for DHCP are "up" and "unknown".

Quoting linux/Documentation/networking/operstates.txt:

  IF_OPER_UNKNOWN (0):
   Interface is in unknown state, neither driver nor userspace has set
   operational state. Interface must be considered for user data as
   setting operational state has not been implemented in every driver.

  ...

  A routing daemon or dhcp client just needs to care for IFF_RUNNING
  or waiting for operstate to go IF_OPER_UP/IF_OPER_UNKNOWN before
  considering the interface / querying a DHCP address.
x-tools: initial support for armv7a tool chain

This patch adds initial support for an armv7a soft-float (no FPU)
toolchain using uclibc.

Verified by compiling a simple 'hello world' program and running under
qemu-arm.

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
armv7a: initial kernel configuration for ARM

Baseline kernel configuration for ARM platforms.

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
busybox-iorw: update iorw command for arm

Add armv7 assembly to the memory barriers used by the iorw command.

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
build system changes to support ARM platform

Adjust and refractor portions of the kernel and ONIE image build
process to accommodate the ARM platform.

For the most part the ARM platform is following the PowerPC model of
using U-Boot with a kernel, initramfs and dtb file.
qemu_armv7a: initial machine configuration

Initial support for ARMv7a based virtual machine.

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>