MFC:	r256932, r256938, r256953

r256932:
Add a new function (OF_getencprop()) that undoes the transformation applied
by encode-int. Specifically, it takes a set of 32-bit cell values and
changes them to host byte order. Most non-string instances of OF_getprop()
should be using this function, which is a no-op on big-endian platforms.

r256938:
A few other common cases for encode-int decoding: OF_getencprop_alloc()
and OF_searchencprop(). I thought about using the element size parameter
to OF_getprop_alloc() to do endian-switching automatically, but it breaks
use with structs and a *lot* of FDT code (which can hopefully be moved to
these new APIs).

r256953:
Fix build.