iwlwifi: work around reverse dependency on MEI

iwlwifi: work around reverse dependency on MEI

If the iwlmei code is a loadable module, the main iwlwifi driver
cannot be built-in:

x86_64-linux-ld: drivers/net/wireless/intel/iwlwifi/pcie/trans.o: in function `iwl_pcie_prepare_card_hw':
trans.c:(.text+0x4158): undefined reference to `iwl_mei_is_connected'

Unfortunately, Kconfig enforces the opposite, forcing the MEI driver to
not be built-in if iwlwifi is a module.

To work around this, decouple iwlmei from iwlwifi and add the
dependency in the other direction.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20211207151447.3338818-1-arnd@kernel.org
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>