buildroot

linux: add probing for kernel version when installing modules

This patch will ask the kernel for the specific version before doing
modules_install, that way Buildroot will know which directories to remove and
what parameters to use for depmod. Needed when compiling a kernel grabbed from
GIT or vendor specific releases.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>