wic: bootimg-efi: Make kernel image installation configurable

wic: bootimg-efi: Make kernel image installation configurable

The issue with installing the kernel image to both rootfs
and boot partition is that some systems rely on the kernel image in
rootfs and not in the boot partition.
This leads to duplication of the kernel image, which can cause
unnecessary storage usage.
This patch provides a solution to the problem by adding a new
parameter "install-kernel-into-boot-dir" to the wic kickstart file.
If this parameter is set to 'true', the plugin will install the
kernel image to the boot partition. If the parameter is set to
'false', the plugin will skip installing the kernel image, avoiding
duplication.

Signed-off-by: Kareem Zarka <kareem.zarka@huawei.com>
Signed-off-by: Christian Taedcke <christian.taedcke@weidmueller.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>