Linux: Update autotools to require KERNEL path

The IPC Linx-side build now requires KERNEL path to be set to
build all libraries and test applications redardless of platform.

This change is needed since rpmsg has been made Linux kernel version
aware.
(cherry picked from commit ffd46a7143ff4e25ea14085b44ff5105c9912769)

Conflicts:
	linux/src/tests/Makefile.am
	linux/src/tests/Makefile.in
	products.mak
12 files changed