PowerPC: Update expected floating point output for gdb.arch/altivec-regs.exp and...

PowerPC: Update expected floating point output for gdb.arch/altivec-regs.exp and gdb.arch/vsx-regs.exp

The format for printing the floating point values was changed by commit:

   commit 56262a931b7ca8ee3ec9104bc7e9e0b40cf3d64e
   Author: Tom Tromey <tromey@adacore.com>
   Date:   Thu Feb 17 13:43:59 2022 -0700

       Change how "print/x" displays floating-point value

       Currently, "print/x" will display a floating-point value by first
       casting it to an integer type.  This yields weird results like:

           (gdb) print/x 1.5
           $1 = 0x1
        ...
        Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16242

The above change results in 417 regression test failures since the expected
Power vector register output no longer match.

This patch updates the expected Altivec floating point register prints to
the hexadecimal format for both big endian and little endian systems.  The
patch also fixes a formatting isue with the decimal_vector expected value
assign statements.

The expected VSX vector_register1, vector_register1_vr, vector_register2,
vector_register2_vr variables are updated to include the new float128 entry.
Additionally, the comment in the vsx expect file about the initialization
of the vs registers is updated.

The patch has been tested on Power 10, Power 8 LE and Power 8 BE.