wifi: nl80211: Add EHT fixed Tx rate support

wifi: nl80211: Add EHT fixed Tx rate support

Add new attributes to support EHT MCS/NSS Tx rates and EHT GI/LTF.
Parse EHT fixed MCS/NSS Tx rates and EHT GI/LTF values passed by the
userspace, validate and add as part of cfg80211_bitrate_mask.

MCS mask is constructed by new function, eht_build_mcs_mask(). Max NSS
supported for MCS rates of 7, 9, 11 and 13 is utilized to set MCS
bitmask for each NSS. MCS rates 14, and 15 if supported, are set only
for NSS = 0.

Co-developed-by: Aloka Dixit <aloka.dixit@oss.qualcomm.com>
Signed-off-by: Aloka Dixit <aloka.dixit@oss.qualcomm.com>
Signed-off-by: Muna Sinada <muna.sinada@oss.qualcomm.com>
Link: https://patch.msgid.link/20250815213011.2704803-1-muna.sinada@oss.qualcomm.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>