kbuild: install all headers when arch is changed

We see some header files that are selected dependent on
the actual architecture so force a reinstallation
of all header files when the arch changes.
This slows down "make headers_check_all" but then
we better reflect reality.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

diff --cc scripts/Makefile.headersinst
Simple merge

diff --cc scripts/headers_install.pl
Simple merge