[xserver-xf86-config] Add machine-specific xorg.conf

Previously, xorg.conf files were shipped in the meta-gumstix-extras
layer rather than the meta-gumstix layer.  As this configuration enables
the display, it seems like something that should be included with the
BSP rather than as an add-on.

Signed-off-by: Ash Charles <ashcharles@gmail.com>
[linux] Use yocto standard linux.inc

We don't need to maintain our own linux.inc when there is a
more up-to-date one provided by the main yocto layer.

Signed-off-by: Ash Charles <ashcharles@gmail.com>
Supply firmware with linux-firmware recipe

Some Overo COMs use a sd8686 or sd8787-based wifi module.  Some DuoVero
COMs and Pepper use a sd8787-based wifi module.  The firmware for these
modules is included with the linux-firmware recipe.  This recipe
produces packages that include firmware files that conflict with files
shipped by the kernel recipe:
http://comments.gmane.org/gmane.linux.embedded.yocto.general/18065.

To ensure only linux-firmware is providing firmware, we adjust the
kernel configs to disable some module pulling in firmware and update
the MACHINE_EXTRA_RDEPENDS.

Signed-off-by: Ash Charles <ashcharles@gmail.com>