wifi: iwlwifi: mld: update link grading tables per bandwidth

wifi: iwlwifi: mld: update link grading tables per bandwidth

Replace single RSSI-to-grade table with separate tables for each
operational bandwidth. Grade selection now depends on both RSSI and
the link's operational bandwidth.

Improve puncturing penalty calculation to apply proportional reduction
based on unusable spectrum percentage rather than absolute channel count.

Update existing KUnit tests with RSSI values for new grading tables.

Signed-off-by: Avinash Bhatt <avinash.bhatt@intel.com>
Tested-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260513084215.9f848b0da851.Id239216fda62e25d343495696cc60742e57d56ea@changeid
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>