configure: improve usbfs check

configure: improve usbfs check

The current check to test if usbfs support should be compiled or not
solely relies on the presence of <linux/usbdevice_fs.h>, without
actually checking that all definition used by Qemu are provided by
this header file.

With sufficiently old kernel headers, <linux/usbdevice_fs.h> may be
present, but some of the definitions needed by Qemu may not be
available.

This commit improves the check by building a small program that
actually tests whether the necessary definitions are available.

In addition, it fixes a bug where have_usbfs was set to "yes"
regardless of the result of the test.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190213211827.20300-1-thomas.petazzoni@bootlin.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>