target-ppc: Define Endian-Correct Accessors for VSR Field Access

target-ppc: Define Endian-Correct Accessors for VSR Field Access

This change defines accessors for VSR doubleword and word fields that
are correct from a host Endian perspective.  This allows code to
use the Power ISA indexing numbers in code.

For example, the xscvdpsxws instruction has a target VSR that looks
like this:

  0           32       64                    127
  +-----------+--------+-----------+-----------+
  | undefined | SW     | undefined | undefined |
  +-----------+--------+-----------+-----------+

VSX helper code will use VsrW(1) to access this field.

Signed-off-by: Tom Musta <tommusta@gmail.com>
Tested-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>