wifi: wcn36xx: Rename clunky firmware feature bit enum

The enum name "place_holder_in_cap_bitmap" is self descriptively asking to
be changed to something else.

Rename place_holder_in_cap_bitmap to wcn36xx_firmware_feat_caps so that the
contents and intent of the enum is obvious.

Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220727161655.2286867-2-bryan.odonoghue@linaro.org