wifi: iwlwifi: pcie: move generation specific files to a folder

As a new generation of pcie is going to be written, we will need a
folder for each generation.
Since gen1 and gen2 code is tightly coupled and has with shared logic -
it is not really separable.
Put the code of both in one folder.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250609211928.bb0757c326c5.I66345c2b3fda55dcb8ff779c64de72d5c19f6649@changeid