fdt: Use bswapN instead of bswap_N

fdt: Use bswapN instead of bswap_N

Fixes the libfdt enabled build for hosts that have <machine/bswap.h>.

The code at the beginning of qemu/bswap.h is attempting to standardize
on bswapN.  In the case of CONFIG_MACHINE_BSWAP_H, this is all we get.
In the case of CONFIG_BYTESWAP_H, we get bswap_N from the system header
and then wrap these with inline functions to get bswapN.

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