wifi: mt76: mt7915: rework eeprom tx paths and streams init

wifi: mt76: mt7915: rework eeprom tx paths and streams init

[ Upstream commit a7ec8bcf00034ce84d4c9a15dffd7577fbed4db2 ]

Rework tx paths and streams init part to improve readability, and make
sure that the available tx streams should be smaller than or equal to
the available tx paths.

Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Stable-dep-of: de147cc28985 ("wifi: mt76: mt7915: Fix chainmask calculation on mt7915 DBDC")
Signed-off-by: Sasha Levin <sashal@kernel.org>