package.bbclass/module-strip.bbclass: Various strip fixes

package.bbclass/module-strip.bbclass: Various strip fixes

* Turn striping functionality into functions and call in the appropriate place
* Removing various races and ordering issues
* Should mean kernel modules are correctly stripped (and stripping can be disabled)
* Addresses bug 1182
* kernel module stripping applied to ${PKGD} (the correct place)

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>