build: strip debug symbols from installed kernel modules

Debug symbols in installed kernel modules consume space
in the target filesystem, so strip them. Modules with
debug symbols should be present in the KERNEL_OBJ
location for debug purposes. 

CRs-fixed: 400053
Change-Id: Ic7f75faf6d44b5bca831c159d7bb09bba6a12b66
Signed-off-by: Nagender Telkar <ntelkar@codeaurora.org>