If compiled with CONFIG_FDT, allow user to specify a device tree file using
the -dtb argument.  If the machine supports it then the dtb will be loaded
into memory and passed to the kernel on boot.
Signed-off-by: NJeremy Kerr <jeremy.kerr@canonical.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
[Peter Maydell: Use machine opt rather than global to pass dtb filename]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>