NXP is probably the best "big" vendor for this. The main issue is that their documentation solution/website is awful.
I think a smaller vendor like Toradex is more in line with what you're asking for though. I haven't used them myself, but I've heard very good things. First class yocto support is a core part of their offering.
The Toradex's, Phytec's, Boundary Devices, etc... of the world all do a decent job with their BSP's but just know that they pull from NXP's mainline BSP release so there is a lag in time from when NXP makes a new release. Sometimes they'll fork their own libraries which I've seen cause some problems with application level software from NXP.
I think a smaller vendor like Toradex is more in line with what you're asking for though. I haven't used them myself, but I've heard very good things. First class yocto support is a core part of their offering.