LU-17504 build: fix array-index-out-of-bounds warning

LU-17504 build: fix array-index-out-of-bounds warning

On Linux kernel 6.5, due to commit 2d47c6956ab3
("ubsan: Tighten UBSAN_BOUNDS on GCC"), flexible
trailing arrays declared like 'lc_array_sum[1];'
will generate warnings when CONFIG_UBSAN & co. is
enabled:

  UBSAN: array-index-out-of-bounds in lprocfs_status.c:1609:17
  index 1 is out of range for type '__s64 [1]'

Since LPROCFS_STATS_FLAG_IRQ_SAFE flag is only used
in one place - obd_memory() counter, we can just
remove it and change obd_memory over to a regular
percpu_counter. This would both simplify the
lprocfs_counter() code, move over to using more
kernel functionality instead of libcfs, as well as
reduce overhead slightly for the memory accounting code.

Change-Id: Ic461c4b30317bfd2b1e9f5b6be84c4a7fb4e3eb9
Signed-off-by: Jian Yu <yujian@whamcloud.com>