firmware: do not use fw_lock for fw_state protection

fw_lock is to use to protect 'corner cases' inside firmware_class. It
is not exactly clear what those corner cases are nor what it exactly
protects. fw_state can be used without needing the fw_lock to protect
its state transition and wake ups.

fw_state is holds the state in status and the completion is used to
wake up all waiters (in this case that is the user land helper so only
one). This operation has to be 'atomic' to avoid races.  We can do this
by using swait which takes care we don't miss any wake up.

We use also swait instead of wait because don't need all the additional
features wait provides.

Note there some more cleanups possible after with this change. For
example for !CONFIG_FW_LOADER_USER_HELPER we don't check for the state
anymore.  Let's to this in the next patch instead mingling to many
changes into this one. And yes you get a gcc warning "‘__fw_state_check’
defined but not used [-Wunused-function] code." for the time beeing.

Cc: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Acked-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>