dtc: Automatically pick a sensible boot_cpuid_phys

[Jon Loeliger]

> Currently, when in -Idts -Odtb or -Ifs -Odtb modes, dtc always
> defaults to using 0 as the value for the boot_cpuid_phys header field.
> That's correct quite often, but there are some systems where there is
> no CPU with hardware ID of 0, or where we don't want to use the CPU
> with hardware ID 0 at all (e.g. for AMP-style partitioning).  The only
> way to override this default currently, is with the -b command line
> option.
> 
> This patch improves dtc to instead base the default boot_cpuid_phys
> value on the reg property of the first listed subnode of /cpus.  This
> means that dtc will get boot_cpuid_phys correct by default in a
> greater proportion of cases (since the boot cpu is usually listed
> first, and this way at least the boot_cpuid_phys default will match
> some existing cpu node).  If the node doesn't exist or has an invalid
> 'reg' property (missing or not 4 bytes in length), then
> boot_cpuid_phys is set to 0.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

jdl