mt76: split single ldpc cap bit into bits

The original single LDPC cap bit cannot be used to
differentiate LDPC cap in each PHY mode.
This modification split the single bit into 3 bits,
ht_ldpc, vht_ldpc, and he_ldpc.

Reviewed-by: Ryder Lee <ryder.lee@mediatek.com>
Suggested-by: Money Wang <Money.Wang@mediatek.com>
Signed-off-by: MeiChia Chiu <MeiChia.Chiu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>