bswap: Rewrite all ld<type>_<endian>_p functions

Use the new host endian unaligned access functions instead of
open coding byte-by-byte references.  Remove assembly special
cases for i386 and ppc -- we've now exposed the operation to
the compiler sufficiently for these to be optimized automatically.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
