prov/psm: clean up the fid_xxx variable names

The names "fid_xxx" have been used inconsistently at different
places. In many cases, "fid_" is used to distinguish variables
of provider private types (e.g. "struct psmx_fid_ep *fid_ep")
from variables of generic fabric types (e.g. "struct fid_ep *ep").
However, this is not done consistently and the "fid_" prefix
doesn't clearly convey such information.

This patch removes the "fid_" prefix from all the variable names.
Use "xxx" whenever possible and use "xxx_priv" for variables of
provider private types when the names "xxx" have already been
used for variables of generic fabric types.

Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>