linux-libc-headers: use kernel-arch.bbclass

linux-libc-headers: use kernel-arch.bbclass

linux-libc-headers recipes all have their own code to set ARCH.
However this same functionality is in kernel-arch.bbclass
This patch adds an inherit kernel-arch in linux-libc-headers.inc
and removes all arch calculation code from the recipes

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Acked-by: Tom Rini <tom_rini@mentor.com>
Acked-by: Chris Larson <chris_larson@mentor.com>