iwlwifi: mvm: BT Coex - allow MIMO in more cases

We can Tx in MIMO rates when we are in TxTx Disallow mode
just like we can when we are in Tight mode.
Same if we are in 5Ghz regardless of the mode we are.
Change the code to allow MIMO in these cases.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>