Support passing a board ID value to the kernel in r1
that is more than 16 bits wide. This is needed to pass
the '-1 == invalid' value for boards which only support
device tree booting.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Tested-by: NMark Langsdorf <mark.langsdorf@calxeda.com>