libpmc: Move libpmc and utils to a new pmc package

[ivy]

Summary

Due to the size of libpmc.so.5, this reduces the size of the -utilities
package by 10%.

MFC after: 3 days

[emaste]

OK, the size savings justify the pkg proliferation here I'd say.

[adrian]

yup, and it also makes churning on libpmc development easier (if I ever do that again :-) )

Thanks!