math/py-cvxpy: fix build on powerpc64

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:70:11: error: unknown type name 'Packet2d'

70 |   typedef Packet2d                        vectortype;
   |           ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:72:23: error: use of undeclared identifier 'Packet2d'

72 |   typedef PacketBlock<Packet2d,2>            rhstype;
   |                       ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:656:44: error: use of undeclared identifier 'Packet2d'

656 | struct dhs_pack<double, Index, DataMapper, Packet2d, StorageOrder, PanelMode, true>
    |                                            ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:723:44: error: use of undeclared identifier 'Packet2d'

723 | struct dhs_pack<double, Index, DataMapper, Packet2d, StorageOrder, PanelMode, false>
    |                                            ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:1250:14: error: unknown type name 'Packet2l'
1250 | const static Packet2l mask21 = { -1, 0 };

|              ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:1267:21: error: unknown type name 'Packet2d'
1267 | EIGEN_ALWAYS_INLINE Packet2d bmask<Packet2d>(const int remaining_rows)

|                     ^

cvxpy/cvxcore/src/../include/Eigen/src/Core/arch/AltiVec/MatrixProduct.h:1267:36: error: use of undeclared identifier 'Packet2d'
1267 | EIGEN_ALWAYS_INLINE Packet2d bmask<Packet2d>(const int remaining_rows)