kbuild: fix silent mode detection for make 4.4 or newer

JIRA: https://issues.redhat.com/browse/RHEL-21819

Starting with GNU make 4.4, command line variable definitions are
included in $MAKEFLAGS. This confuses the silent build detection code in
the main Makefile, and the side effect is that any command line variable
definition that contains the 's' character (in either the variable name
or the name) will cause the build to be silent.

This problem has been already found and fixed upstream. Backport the
relevant changes to the RHEL kernel to prevent issues with newer
versions of make.

Signed-off-by: Radu Rendec rrendec@redhat.com