ipmi_flash.md: update docs to include fileOpen state
ipmi_flash.md: update docs to include fileOpen state

Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>
Change-Id: Ia45e55dc5192be9c1564d5fbd78b16b1c53156a6

openbmc/phosphor-ipmi-flash