iwlwifi: avoid d0i3 commands when no/init ucode is loaded

d0i3 commands are not supported in the init image, so take
a reference to ensure we don't enter d0i3 during init image,
and additional checks to prevent d0i3 commands when no
fw image is loaded.

Add a few WARN_ON_ONCE to the d0i3 enter/exit commands
to ensure we send d0i3 commands only when the normal
ucode is loaded.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>