build: Fix missing MAKEFLAGS --no-print-directory

build: Fix missing MAKEFLAGS --no-print-directory

While we already have "--no-print-directory" added to the make flags
in some cases, there's one case where the flags is missing, when doing
an out-of-tree build with O=, e.g.
    cd xen; make O=build

Without it, we just have loads of "Entering directory" and "Leaving
directory" with the same directory.

The comment and location in the Makefile are copied from Linux.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>