Partially revert my recent kernelPackages changes

First, pass in `self' again so that overriding works properly (thanks
for pointing that out, @edolstra)

Second, instead of having linuxPackages*.kernel mean something different
inside the set and out, add a new attribute linuxPackages*.kernelDev,
which for the generic kernel is simply linuxPackages*.kernel but for the
manual-config kernel is the `dev' output (which has the build tree,
source tree, etc.)

The second change required trivial modifications in a bunch of
expressions, I verified that all of the linuxPackages* sets defined in
all-packages.nix have the same drv paths before and after the change.

Signed-off-by: Shea Levy <shea@shealevy.com>