linux-yocto: Add kernel hardening by default

Add kernel hardening options based on the Kernel Self Protection Project
recommendations [1] and set them in the default kernel.

[1] https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings



Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>