[FEA] Implement wrapper around spdlog in rmm

[vyasr]

Is your feature request related to a problem? Please describe.
Currently rmm's logger uses spdlog directly. This approach is problematic because it makes spdlog a dependency of every consumer of rmm. spdlog the library is not inherently problematic, but its centrality makes it a troublesome dependency to deal with in a packaging sense because of the web of constraints it imposes on a dependency tree.

Describe the solution you'd like
As part of rapidsai/build-planning#104, we should first explore how to make spdlog a non-transitive dependency of rmm. In order to accomplish this, we will have to isolate the dependence to something like an inline header that is intended to be compiled into a unique TU by the consumer.