iwlwifi: add csr configuration for 6300 devices

Recently we have switched the csr addresses and values configuration
from a single configuration to all devices to a per-device configuration.
Doing that, the configuration for 6300 devices wasn't set.
This missing definition introduced a kernel panic once trying to access
the csr's.

Add the missing 6300 csr configuration.

While at it, add a checker that the csr values were indeed
configured, and bail out more gracefully if not.

Fixes: a8cbb46f ("iwlwifi: allow different csr flags for different device families")
Signed-off-by: Golan Ben Ami <golan.ben.ami@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>