input: atmel_mxt_ts_mmi: Use atomic "suspended" flag

Change flag "suspended" to atomic, to fix races with multiple suspend
and resume callers.

Also, use a different "poweron" flag instead of suspend, to decide how
to deal with the interrupt, since the order of setting/clearing the
suspended flag doesn't line up with the intended usage.

Signed-off-by: Chris Fries <cfries@motorola.com>