A couple of people have wanted to create and maintain BSPs based on their own kernels via linux-yocto-custom, so we should add that as one of the kernel options for the yocto-bsp tool.
Implemented by poky/master commits: 9753196c77d7b65ae172333a81c18d4dea34f2ca through 0be41d6e30e6dfd9d77e7b8b7ca11ab0b8474cbb
Verified in 1.4M3.