build: Restructure the kernel filter
build: Restructure the kernel filter

Stash the kernel image in a local buffer and
flush it out once done.

This is preparation work for supporting uncompressed
kernels in the next commit.

Signed-off-by: Rolf Neugebauer <bc755ac45a0e799d1d490cba76febc56d80cc5fc@rneugeba.io>

rn/linuxkit,djs55/linuxkit,JohnnyLeone/linuxkit,furious-luke/linuxkit,linuxkit/linuxkit,konstruktoid/linuxkit,linuxkit/linuxkit,konstruktoid/linuxkit,konstruktoid/linuxkit,deitch/linuxkit,deitch/linuxkit,rn/linuxkit,rn/linuxkit,yankcrime/linuxkit,deitch/linuxkit,justincormack/linuxkit,furious-luke/linuxkit,djs55/linuxkit,yankcrime/linuxkit,rn/linuxkit,rn/linuxkit,JohnnyLeone/linuxkit,linuxkit/linuxkit,furious-luke/linuxkit,djs55/linuxkit,justincormack/linuxkit,justincormack/linuxkit,yankcrime/linuxkit,justincormack/linuxkit,linuxkit/linuxkit,furious-luke/linuxkit,djs55/linuxkit,justincormack/linuxkit,deitch/linuxkit,djs55/linuxkit,JohnnyLeone/linuxkit,furious-luke/linuxkit,justincormack/linuxkit,konstruktoid/linuxkit,JohnnyLeone/linuxkit,yankcrime/linuxkit,yankcrime/linuxkit,konstruktoid/linuxkit,linuxkit/linuxkit,yankcrime/linuxkit,deitch/linuxkit,JohnnyLeone/linuxkit,konstruktoid/linuxkit