LU-9855 obdclass: simplify md_stats code

LU-9855 obdclass: simplify md_stats code

The md_stats code is layered in many levels of macros that make
the code difficult to read as well as introduce undetected
errors. This peels away the macro wrappers by replacing it with
the function lprocfs_exp_count_increment() which doesn't care
about the order of the function pointers in struct md_ops. The
other change is macros used for initializing the counters. This
is done by replacing lprocfs_init_mps_stats() with very simple
handling in lprocfs_alloc_md_stats().

Change-Id: I036ce4518ffb08d53e2d27bcdea564a4c799181d
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/32822
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>