pimgen: Add command positional argument
pimgen: Add command positional argument

In preparation for enabling additional commands.

Change-Id: I16ec80c9b8f7eebcfd1a47c6ab7b7fe0e581123b
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>

openbmc/phosphor-inventory-manager,openbmc/phosphor-inventory-manager