staging: fix olpc_dcon kconfig and build errors

drivers/staging/olpc_dcon/olpc_dcon_xo_1_5.c:106: error: 'acpi_gbl_FADT' undeclared (first use in this function)

Fixing that one gives:

ERROR: "backlight_device_register" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!
ERROR: "registered_fb" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!
ERROR: "lock_fb_info" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!
ERROR: "backlight_device_unregister" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!
ERROR: "num_registered_fb" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!
ERROR: "fb_blank" [drivers/staging/olpc_dcon/olpc-dcon.ko] undefined!

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Chris Ball <cjb@laptop.org>
Cc: Jon Nettleton <jon.nettleton@gmail.com>
Acked-By: Andres Salomon <dilinger@queued.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>