dtc: Use stdint.h types throughout dtc

Currently, dtc defines Linux-like names for various fixed-size integer
types.  There's no good reason to do this; even Linux itself doesn't
use these names for externally visible things any more.  This patch
replaces these with the C99 standardized type names from stdint.h.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>