suite-sparse: add 5.4.0, 5.5.0, and 5.6.0, GitHub releases (#14547)

- The suite-sparse author publishes new versions starting with 5.5.0 on GitHub, see https://github.com/DrTimothyAldenDavis/SuiteSparse/releases and http://faculty.cse.tamu.edu/davis/SuiteSparse/
  - change spack to download from there
  - updated sha256 checksums from GitHub for all available releases
- For versions 5.4.0, 5.5.0, 5.6.0 there is a slightly different compilation necessary: first `make default` then `make install`.

Summary of the version changes (+ added, -removed [because not available on GitHub]):
```
+ 5.6.0
+ 5.5.0
+ 5.4.0
  5.3.0
  5.2.0
+ 5.1.2
  5.1.0
+ 5.0.0
+ 4.5.6
  4.5.5
- 4.5.4
  4.5.3
- 4.5.1
```