[PATCH] Support select-cc for VSFRC when VSX is enabled

A previous patch enabled SELECT_VSRC and SELECT_CC_VSRC for VSX to
handle <2 x double> cases.  This patch adds SELECT_VSFRC and
SELECT_CC_VSFRC to allow use of all 64 vector-scalar registers for the
f64 type when VSX is enabled.  The changes are analogous to those in
the previous patch.  I've added a new variant to vsx.ll to test the
code generation.

(I also cleaned up a little formatting in PPCInstrVSX.td from the
previous patch.)