Allow platform vendors to take precedence having their own max rtt support.
This makes sense because the host controller's nortt characteristic may
vary among vendors.

while at it, set this value for Mediatek, as requested by Peter -
https://lore.kernel.org/all/0a57d6bab739d6a10584f2baba115d00dfc9c94c.camel@mediatek.com/Signed-off-by: Avri Altman <avri.altman@wdc.com>
Link: https://lore.kernel.org/r/20240530142510.734-3-avri.altman@wdc.comReviewed-by: Peter Wang <peter.wang@mediatek.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>