dist/tools/esptools: add support for installing esp8266 toolchain

[benpicco]

Contribution description

esptools provide a handy way to quickly install the toolchain needed for the various ESP32 family members.

Installing the toolchain for the venerable esp8266 always requires looking up the right wiki page since it uses a custom toolchain that does not follow the same format.

To streamline this, add a special case for esp8266 to the install.sh script so the same script can be used to get all the Espressif toolchains.

Testing procedure

Simply run

./dist/tools/esptools/install.sh esp8266

and

./dist/tools/esptools/export.sh esp8266

Issues/PRs references

[riot-ci]

Murdock results

:heavy_check_mark: PASSED

a5b437cd25545ed83b436752eeec69fc5fc51035 dist/tools/esptools: make export.sh more helpful

Success	Failures	Total	Runtime
1	0	1	01m:17s

Artifacts

• Documentation preview

[benpicco]

I also took the opportunity to add some more output to export.sh - I think for most users it's not obvious that this an ephemerial change only.