Adds support for config fragments - small diffs which define what kernel config options must be disabled/enabled.
Use $_kconfig_name to define the base defconfig. Note: "$_config" must be removed from APKBUILD.
Diff must be named "$_kconfig_name.$arch"
Example: for base defconfig
sprd_sharkl3_defconfig and arch
aarch64 the file name will be
The file needs to be created manually (e.g. with touch), it can be empty.