module.bbclass: Create a new depmodwrapper to assist cross-installs

Previously the build path to STAGING_KERNEL_DIR was being embedded into the
package post install scripts.  We avoid this behavior by generating a special
depmodwrapper script.  This script contains that hard-coded path, ensuring
that re-use of the sstate-cache (and/or packages) will always run through the
wrapper generated by the current build with a checksum that includes
STAGING_KERNEL_DIR.

[ YOCTO #3962 ]

(From OE-Core rev: b18c61bae4d7161c087a004bba3c696006f7a2f6)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Conflicts:

	meta/classes/image.bbclass
	meta/classes/kernel.bbclass
depmodwrapper-cross: Mark as machine specific

The kernel and its staging directory are machine specific so the wrapper
needs to be as well. Also take the opportunity to remove the default
dependencies of the recipe since its a script and doesn't need the cross
compiler. This gives the build a little more scheduing freedom.

(From OE-Core rev: 1cc2ac769baae19b54184df5f43a3e77c1743c29)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>