target-ppc: implement lxv/lxvx and stxv/stxvx

target-ppc: implement lxv/lxvx and stxv/stxvx

lxv:  Load VSX Vector
lxvx: Load VSX Vector Indexed

    Little/Big-endian Storage
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    Vector load results:
    BE:
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    LE:
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |E7|E6|E5|E4|E3|E2|E1|E0|F7|F6|F5|F4|F3|F2|F1|F0|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

stxv: Store VSX Vector
stxvx: Store VSX Vector Indexed

    Vector (8-bit elements) in BE:
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    Vector (8-bit elements) in LE:
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |E7|E6|E5|E4|E3|E2|E1|E0|F7|F6|F5|F4|F3|F2|F1|F0|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    Store results in following:
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |F0|F1|F2|F3|F4|F5|F6|F7|E0|E1|E2|E3|E4|E5|E6|E7|
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>