target/ppc: introduce GEN_VSX_HELPER_X3 macro to fpu_helper.c

target/ppc: introduce GEN_VSX_HELPER_X3 macro to fpu_helper.c

Rather than perform the VSR register decoding within the helper itself,
introduce a new GEN_VSX_HELPER_X3 macro which performs the decode based
upon xT, xA and xB at translation time.

With the previous changes to the VSX_CMP generator and helper macros the
opcode parameter is no longer required in the common case and can be
removed.

Signed-off-by: Mark Cave-Ayland <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <20190616123751[email protected]>
Signed-off-by: David Gibson <[email protected]>