iwlwifi: rs: disable MIMO only if allowed in configuration

Fix bug where MIMO is disabled for low latency TX on P2P VIF
regardless of configuration. Make it dependent on
IWL_MVM_RS_DISABLE_P2P_MIMO compilation option. Change configuration
so that MIMO will be disabled only in SDIO platforms.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>