MFC r357923-r357924: dtc fixes for /memreserve/ and -I/-O defaults

r357923:
Pull in latest fixes from dtc, up to 0060471

This includes a small battery of /memreserve/ fixes to make sure dtc is
properly writing these regions into the output file and reading them back
out.

As of this update, dtc will now also assume common defaults for -I/-O if
only one is specified; namely, dts for one implies dtb for the other and
vice versa (Requested by: jhibbits, preserves GPL dtc behavior too).

r357924:
dtc: re-apply r353961, r354115

I missed in final review of r357923's diff that these ones hadn't yet been
sent upstream and inadvertently reverted them. =-( Re-apply now.