Fix incomplete RESPONSE_[RESOURCE|JOB_PACK]_ALLOCATION building path.

There were two code paths building an allocation response by calling
its own static _build_alloc_msg() function:

1. src/slurmctld/proc_req.c
2. src/slurmctld/srun_comm.c

These two functions diverged and both had members that were not filled
in but were filled in the other. This patch makes it so we change the
signature of the one in proc_req.c to make it extern and then in
srun_comm.c we call this newly common function.

Also added cpu_freq_[min|max|gov] members in the common one since these
were the only members missing in proc_req.c function (the one in
srun_comm.c had more members missing, like all the ntasks_per*, account,
qos or resv_name).

Bug 4999.