iwlwifi: mvm: get NVM later in the mvm_start flow

iwlwifi: mvm: get NVM later in the mvm_start flow

We don't need the NVM until fairly late in the flow and
since this flow will be split soon, get the NVM later to
unite it with the parts that really need it.
Gather all what needs the NVM into a function.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210210171218.bab0e65c4909.I789f3eb577b216ad1688269e036ce9fa4880f532@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>