[formatv2] add support for toolchains with a version suffix (e.g. goalf-1.1.0-no-OFED)

[boegel]

This is a TODO for easyconfig format v2.x, somewhat non-urgent for now.

[boegel]

e.g.:

[SUPPORTED]
toolchains = goalf == 1.1.0; versionsuffix:-no-OFED

Potential problem: allowing to use a toolchain with a versionsuffix for a dependency:

[DEPENDENCIES]
zlib = 1.2.7, goalf == 1.1.0; versionsuffix:-no-OFED

With this syntax, it's not clear whether the versionsuffix applies to zlib or the custom toolchain goalf...