staging: fsl-mc/dpio: add cpu <--> LE conversion for dpaa2_fd

While dpaa2_fd.simple structure fields are marked __leXX,
corresponding cpu_to_leXX / leXX_to_cpu conversions are missing.

While here, fix dpaa2_fd_{get,set}_bpid such that BMT, IVP bits
sharing the 16-bit field with BPID are not affected.

Fixes: d3269bdc

 ("bus: fsl-mc: dpio: add frame descriptor and scatter/gather APIs")
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>