Fix workspace query for *syevd and *heevd routines

[neil-lindquist]

Description

The optimal workspace for dsytrd is n*nb where nb is the blocksize provided by ilaenv. However, when dsyevd is called with lwork=-1, the requested workspace size is only 2*n + nb (2*n is needed to hold the tridiagonal matrix).
So, dsyevd will use the unblocked dsytrd unless the user knows to provide extra workspace, regardless of how well ilaenv is tuned.

The issue is also present in ssyevd, cheevd, and zheevd.

This PR corrects dsyevd et al. to request enough workspace to use a blocked tridiagonal reduction.

Checklist

• The documentation has been updated.
• If the PR solves a specific issue, it is set to be closed on merge.

[weslleyspereira]

Thanks @neil-lindquist!