tools/testing/nvdimm: Emulate firmware activation commands

Augment the existing firmware update emulation to track activations and
validate proper update vs activate sequencing.

The DIMM firmware activate capability has a concept of a maximum amount
of time platform firmware will quiesce the system relative to how many
DIMMs are being activated in parallel. Simulate that DIMM activation
happens serially, 1 second per-DIMM, and limit the max at 3 seconds. The
nfit_test0 bus emulates 5 DIMMs so it will take 2 activations to update
all DIMMs.

Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Reported-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>