pcu: Add infra to handle multitrx and multits envs

ARFCNs are allocated sequentially, so that conversion between
arfcn<->trx_nr is easily done.

Some helper functions are introduced to be able to submit and expect
messages on a given TRX+TS, which is required for setups with several
TRX and PDCH-enabled TS different than the default. These new APIs
will be used in PCU_Tests.ttcn in subsequent patches.

Change-Id: I28430e6d8c77d2b7dc630d186d425a5d82587b82
3 files changed