cmake: Used syntax mismatches minimum_required version

[sbngross]

install commands in src/CMakeLists.txt have the TYPE attribute. This syntax was introduced in cmake 3.14

minimum_required_version is 3.12.

Came across it when I tested my PR with a stone-age debian 10. There is a cmake 3.13.
It just runs in qemu so I can't provide logs, but this error is obvious.

The question remains how to deal with it. Raise min_req_ver or get rid of new syntax?

PS: We had to adapt the man install anyway to the DESTINATION syntax for #1063

[mcuee]

I tend to think it is easier to raise the minimum_required_version to 3.14. But let's hear from @mariusgreuel or @dl8dtl.

[mcuee]

@mariusgreuel
Please help to check this one. Thanks.