For building kernel or to get boot-yocto image:
Download latest release according to your PC(I have used Linux ubuntu 16.04) of 64 bit.
Unzip the file.you will get legato-spm tool.
Run "legato-spm --install --module WP750X --update-link "
Run “legato-spm --install --module WP750X --sdk pdk.64”
there will be “legato.source.”
Enter into that directory and give “make”(It will take >1 Hr max).
later create build environment for kernel configuration for that you need to use below commands:
source poky/oe-init-build-env build_bin
. poky to get build_env
bitbake linux-yocto -c menuconfig
bitbake -c linux-yocto compile
Run Once again “make” to reflect the configurations changed in the flashing image.