resin-os.inc: Add initramfs configuration
resin-os.inc: Add initramfs configuration

We build the initramfs with the kernel image. As well we set the
initramfs extension name as '-initramfs' so that boards (like
RaspberryPi) can use it when adding files to boot partition.

Signed-off-by: Andrei Gherzan <8dc7c09356db0b1762fb140617d7375c0a5a4131@resin.io>
Signed-off-by: Theodor Gherzan <be3f40ffe21d83aefcbc279c996fd6bca5445244@resin.io>

resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin