Automate kernel builds + bundle modules

Configure buildroot to automatically build our kernel (and as a side
effect, get the kernel modules into the rootfs image).  While we're at
it, defconfig-ify kernel_config.

For now, we reference the tarball at
  <http://n900.quitesimple.org/rescueOS/sourcecode/kernel_source.tar.gz>
which is equivalent to commit
  a91ce11c777f31ec3d04e60506bcd224f448382e
from the former MeeGo N900 device adaptation project.

buildrootconfig

@@ -33,3 +33,9 @@ BR2_PACKAGE_WPA_SUPPLICANT_CLI=y
 BR2_PACKAGE_WPA_SUPPLICANT_PASSPHRASE=y
 BR2_PACKAGE_BASH=y
 BR2_PACKAGE_NANO=y
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
+BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="http://n900.quitesimple.org/rescueOS/sourcecode/kernel_source.tar.gz"
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="../N900_RescueOS/kernel_config"
+BR2_LINUX_KERNEL_ZIMAGE=y