devtool: fix modify with patches in override directories

If a recipe applies patches which are in machine-specific override
directories, devtool will fail to fetch the patches that don't match the
default configuration.  For example where there are patches at
qemux86/x86.patch and qemuarm/arm.patch:

SRC_URI = "file://source"
SRC_URI_append_qemuarm = " file://arm.patch"
SRC_URI_append_qemux86 = " file://x86.patch"

The patch apply phase sets OVERRIDES but does not set FILESOVERRIDES, so
it cannot find the patch files as the search path isn't correct.  Fix
this by setting FILESOVERRIDES too.

Also when iterating through the overrides we need to be sure that other
overrides that are used are not enabled, so extend no_overrides instead of
simply appending the current override.

Fixes most but not all of [ YOCTO #14060 ].

(From OE-Core rev: a372cdf8)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 4a35bcc9d164ac038a31356a15a0f61ccdd38be2)
Signed-off-by: Enrico Jorns <ejo@pengutronix.de>
Signed-off-by: Steve Sakoman <steve@sakoman.com>