bswap.h: Rename ldl_p, stl_p, etc to ldl_he_p, stl_he_p, etc

We have an unfortunate naming clash between the functions
ldl_p, stl_p, etc defined in bswap.h (which have semantics
"load/store in host endianness") and the #defines of the same
name in cpu-all.h (which have the semantics "load/store in
target endianness").

Fortunately it turns out that the only users of the bswap.h
functions are all within bswap.h itself, so we can simply
rename them to include a _he_ infix for "host endianness".

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>